Sequence mapping method and apparatus in wireless communication system

ABSTRACT

A method for mapping a sequence in a wireless communication system includes determining one or more resource blocks to which the sequence will be mapped, and mapping a plurality of modulation symbols to a plurality of resource elements included in the resource blocks, wherein the resource elements are positioned in regions other than OFDM symbol regions indicated by a physical control format indicator channel (PCHICH).

This application is a 35 USC §371 National Stage entry of InternationalApplication No. PCT/KR2012/005927, filed on Jul. 25, 2012, which claimspriority to U.S. Provisional Application No. 61/511,991, filed on Jul.27, 2011, U.S. Provisional Application No. 61/525,201, filed on Aug. 19,2011, U.S. Provisional Application No. 61/532,108, filed on Sep. 8,2011, and U.S. Provisional Application No. 61/551,451, filed on Oct. 26,2011, each of which are hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to a sequence mapping method and apparatusin a wireless communication system.

BACKGROUND ART

Extensive research has been conducted to provide various types ofcommunication services including voice and data services in wirelesscommunication systems. In general, a wireless communication system is amultiple access system that supports communication with multiple usersby sharing available system resources (e.g. bandwidth, transmit power,etc.) among the multiple users. The multiple access system may adopt amultiple access scheme such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and apparatusfor mapping sequences, generated from reception acknowledgement for oneor more transport blocks, to resource elements.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

Technical Solution

In accordance with a first aspect of the present invention, a method formapping a sequence in a wireless communication system includesdetermining one or more resource blocks to which the sequence will bemapped, and mapping a plurality of modulation symbols to a plurality ofresource elements included in the resource blocks, wherein the resourceelements are positioned in regions other than OFDM symbol regionsindicated by a physical control format indicator channel (PCHICH).

In accordance with a second aspect of the present invention, an eNB in awireless communication system includes a transmission module and aprocessor, wherein the processor is configured to determine one or moreresource blocks to which a sequence will be mapped and to map aplurality of modulation symbols to a plurality of resource elementsincluded in the resource blocks, wherein the resource elements arepositioned in regions other than OFDM symbol regions indicated by aPCFICH.

The first and second aspects of the present invention may include all orsome of the following.

The resource blocks may be allocated to a UE that receives the sequence.

The resource blocks may include a resource block that is not allocatedto the UE receiving the sequence.

The resource blocks may correspond to all resource blocks included in acorresponding frequency band.

A start index of the resource elements to which the plurality ofmodulation symbols are mapped may be determined depending on a cellidentifier.

The mapping of the plurality of modulation symbols may comprisesequentially mapping the plurality of modulation symbols to theplurality of resource elements in the frequency domain or in the timedomain.

The mapping of the plurality of modulation symbols may comprise groupingthe plurality of modulation symbols into a plurality of groups eachincluding n modulation symbols, and mapping the plurality of groups tothe plurality of resource elements in the frequency domain or in thetime domain.

Each of the plurality of groups may be mapped with n resource elementsinterval in the plurality of resource elements.

The mapping of the plurality of modulation symbols may comprise mappingthe modulation symbols to resource elements adjacent to resourceelements mapped to reference signals in the resource blocks.

When the resource blocks are not allocated to the UE receiving thesequence, information about at least one of an OFDM symbol or asubcarrier in which mapping of the resource elements is started may betransmitted to the UE.

The plurality of modulation symbols may be generated from receptionacknowledgement for one or more transport blocks.

The one or more transport blocks may be mapped to two or more layers andtransmitted on a physical uplink shared channel.

Advantageous Effects

According to embodiments of the present invention, it is possible toefficiently map an ACK/NACK signal generated when an ePHICH isintroduced to a time-frequency resource.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description taken in conjunction with theaccompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 illustrates a radio frame structure;

FIG. 2 illustrates a resource grid in a downlink slot;

FIG. 3 illustrates a downlink subframe structure;

FIG. 4 illustrates an uplink subframe structure;

FIG. 5 illustrates mapping of PUCCH formats to uplink physical resourceblocks;

FIG. 6 is a diagram illustrating a downlink reference signal;

FIG. 7 is a diagram illustrating carrier aggregation;

FIG. 8 is a diagram illustrating cross carrier scheduling;

FIG. 9 illustrates heterogeneous deployment;

FIGS. 10 and 11 illustrate schemes for alleviating interference throughscheduling in a heterogeneous network;

FIGS. 12 to 15 are diagrams illustrating schemes for generating asequence of modulation symbols for coherent detection according toembodiments of the present invention;

FIGS. 16 and 17 are diagrams illustrating schemes for generating asequence of modulation symbols for non-coherent detection according toembodiments of the present invention;

FIG. 18 illustrates mapping of a modulation symbol sequence in an RBallocated to a specific UE;

FIGS. 19 and 20 are diagrams illustrating frequency-domain-first mappingmethods according to embodiments of the present invention;

FIGS. 21 and 22 are diagrams illustrating time-domain-first mappingmethods according to embodiments of the present invention;

FIG. 23 is a diagram illustrating methods for mapping a sequence to theentire frequency band according to embodiments of the present invention;and

FIG. 24 illustrates configurations of an eNB and a UE according to anembodiment of the present invention.

BEST MODE

Embodiments described hereinbelow are combinations of elements andfeatures of the present invention. The elements or features may beconsidered selective unless otherwise mentioned. Each element or featuremay be practiced without being combined with other elements or features.Further, an embodiment of the present invention may be constructed bycombining parts of the elements and/or features. Operation ordersdescribed in embodiments of the present invention may be rearranged.Some constructions of any one embodiment may be included in anotherembodiment and may be replaced with corresponding constructions ofanother embodiment.

In the embodiments of the present invention, a description is made,centering on a data transmission and reception relationship between aneNB and a user equipment (UE). The eNB is a terminal node of a network,which communicates directly with a UE. In some cases, a specificoperation described as performed by the eNB may be performed by an uppernode of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including an eNB, various operations performed forcommunication with a UE may be performed by the eNB, or network nodesother than the eNB. The term ‘base station (BS)’ may be replaced withthe term ‘fixed station’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’,‘Access Point (AP)’, etc. The term ‘UE’ may be replaced with the term‘terminal’, ‘Mobile Station (MS)’, ‘Mobile Subscriber Station (MSS)’,‘Subscriber Station (SS)’, etc.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention can be supported by standarddocuments disclosed for at least one of wireless access systems,Institute of Electrical and Electronics Engineers (IEEE) 802, 3^(rd)Generation Partnership Project (3GPP), 3GPP Long Term Evolution (3GPPLTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are notdescribed to clarify the technical features of the present invention canbe supported by those documents. Further, all terms as set forth hereincan be explained by the standard documents.

Techniques described herein can be used in various wireless accesssystems such as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier-FrequencyDivision Multiple Access (SC-FDMA), etc. CDMA may be implemented as aradio technology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented as a radio technology such as GlobalSystem for Mobile communications (GSM)/General Packet Radio Service(GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may beimplemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a partof Universal Mobile Telecommunication System (UMTS). 3GPP LTE is a partof Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA fordownlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.WiMAX can be described by the IEEE 802.16e standard (WirelessMetropolitan Area Network (WirelessMAN-OFDMA Reference System) and theIEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity,this application focuses on the 3GPP LTE/LTE-A system. However, thetechnical features of the present invention are not limited thereto.

FIG. 1 illustrates a radio frame structure used in a 3GPP LTE system.Referring to FIG. 1(a), one radio frame may be divided into 10subframes, each subframe including two slots in the time domain. Thetransmission time of one subframe is defined as a Transmission TimeInterval (TTI). For example, one subframe may be 1 ms long and one slotmay be 0.5 ms long. One slot may include a plurality of orthogonalfrequency division multiplexing (OFDM) symbols in the time domain.Because the 3GPP LTE system uses orthogonal frequency division multipleaccess (OFDMA) for downlink, an OFDM symbol may represent one symbolperiod. An OFDM symbol may be regarded as a single carrier-frequencydivision multiple access (SC-FDMA) symbol or symbol period for uplink. AResource Block (RB) is a resource allocation unit including a pluralityof contiguous subcarriers in one slot. This radio frame structure isexemplary. Accordingly, the number of subframes included in a radioframe, the number of slots included in a subframe, and the number ofOFDM symbols included in a slot may vary.

FIG. 1(b) illustrates the type-2 radio frame structure. The type-2 radioframe includes two half frames each having 5 subframes, a downlink pilottime slot (DwPTS), a guard period (GP), and an uplink pilot time slot(UpPTS). Each subframe includes two slots. The DwPTS is used for initialcell search, synchronization, or channel estimation in a UE, whereas theUpPTS is used for channel estimation in an eNB and uplink transmissionsynchronization in a UE. The GP is a period between downlink and uplink,for eliminating interference with the uplink caused by multi-path delayof a downlink signal.

The aforementioned radio frame structure is purely exemplary and thusthe number of subframes included in a radio frame, the number of slotsincluded in a subframe, or the number of symbols included in a slot mayvary.

FIG. 2 illustrates a resource grid in a downlink slot. While FIG. 2shows that a downlink slot includes 7 OFDM symbols in the time domainand each RB has 12 subcarriers in the frequency domain, the presentinvention is not limited thereto. For example, one slot can include 7OFDM symbols in a normal cyclic prefix (CP) case whereas one slot caninclude 6 OFDM symbols in an extended CP case. Each element in theresource grid is referred to as a resource element (RE). An RB includes12×7 REs. The number of RBs per downlink slot, N^(DL) depends ondownlink transmission bandwidth. An uplink slot structure may correspondto the downlink slot structure.

FIG. 3 illustrates a downlink subframe structure. Referring to FIG. 3,OFDM symbols at the start of a downlink subframe are used for a controlregion to which a control channel is allocated and the other OFDMsymbols of the downlink subframe are used for a data region to which aphysical downlink shared channel (PDSCH) is allocated. Downlink controlchannels used in an LTE system include a physical control formatindicator channel (PCFICH), a physical downlink control channel (PDCCH),a physical hybrid automatic repeat request indicator channel (PHICH),etc.

The PCFICH is located in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe.

The PHICH delivers a HARQ acknowledgment/negative acknowledgment(ACK/NACK) signal in response to an uplink transmission.

The PDCCH transmits downlink control information (DCI). The DCI mayinclude uplink or downlink scheduling information or an uplink transmitpower control command for an arbitrary UE group according to format.

DCI Format

DCI formats 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A and 4 are definedin LTE-A (release 10). DCI formats 0, 1A, 3 and 3A have the same messagesize to reduce the number of blind decoding operations, which will bedescribed later. The DCI formats may be divided into i) DCI formats 0and 4 used for uplink scheduling grant, ii) DCI formats 1, 1A, 1B, 1C,2A, 2B and 2C used for downlink scheduling allocation, and iii) DCIformats 3 and 3A for power control commands according to purpose ofcontrol information to be transmitted.

DCI format 0 used for uplink scheduling grant may include a carrierindicator necessary for carrier aggregation which will be describedlater, an offset (flag for format 0/format 1A differentiation) used todifferentiate DCI formats 0 and 1A from each other, a frequency hoppingflag that indicates whether frequency hopping is used for uplink PUSCHtransmission, information about resource block assignment, used for a UEto transmit a PUSCH, a modulation and coding scheme, a new dataindicator used to empty a buffer for initial transmission with respectto an HARQ process, a transmit power control (TPC) command for ascheduled PUSCH, information on a cyclic shift for a demodulationreference signal (DMRS) and OCC index, and an uplink index and channelquality indicator request necessary for a TDD operation, etc. DCI format0 does not include a redundancy version, differently from DCI formatsrelating to downlink scheduling allocation, because DCI format 0 usessynchronous HARQ. The carrier indicator is not included in DCI formatswhen cross-carrier scheduling is not used.

DCI format 4 is newly added to DCI formats in LTE-A release 10 andsupports application of spatial multiplexing to uplink transmission inLTE-A. DCI format 4 has a larger message size because it furtherincludes information for spatial multiplexing. DCI format 4 includesadditional control information in addition to control informationincluded in DCI format 0. DCI format 4 includes information on amodulation and coding scheme for the second transmission block,precoding information for multi-antenna transmission, and soundingreference signal (SRS) request information. DCI format 4 does notinclude the offset for format 0/format 1A differentiation because it hasa size larger than DCI format 0.

DCI formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B and 2C for downlink schedulingallocation may be divided into DCI formats 1, 1A, 1B, 1C and 1D that donot support spatial multiplexing and DCI formats 2, 2A, 2B and 2C thatsupport spatial multiplexing.

DCI format 1C supports only frequency contiguous allocation as compactfrequency allocation and does not include the carrier indicator andredundancy version, compared to other formats.

DCI format 1A is for downlink scheduling and random access procedure.DCI format 1A may include a carrier indicator, an indicator thatindicates whether downlink distributed transmission is used, PDSCHresource allocation information, a modulation and coding scheme, aredundancy version, a HARQ processor number for indicating a processorused for soft combining, a new data indicator used to empty a buffer forinitial transmission with respect to a HARQ process, a TPC command for aPUCCH, an uplink index necessary for a TDD operation, etc.

DCI format 1 includes control information similar to that of DCI format1A. DCI format 1 supports non-contiguous resource allocation whereas DCIformat 1A supports contiguous resource allocation. Accordingly, DCIformat 1 further includes a resource allocation header, and thusslightly increases control signaling overhead as a trade-off for anincrease in resource allocation flexibility.

Both DCI formats 1B and 1D further include precoding information,compared to DCI format 1. DCI format 1B includes PMI acknowledgement andDCI format 1D includes downlink power offset information. Most controlinformation included in DCI formats 1B and 1D corresponds to that of DCIformat 1A.

DCI formats 2, 2A, 2B and 2C include most control information includedin DCI format 1A and further include information for spatialmultiplexing. The information for spatial multiplexing includes amodulation and coding scheme for the second transmission block, a newdata indicator, and a redundancy version.

DCI format 2 supports closed loop spatial multiplexing and DCI format 2Asupports open loop spatial multiplexing. Both DCI formats 2 and 2Ainclude precoding information. DCI format 2B supports dual layer spatialmultiplexing combined with beamforming and further includes cyclic shiftinformation for a DMRS. DCI format 2C may be regarded as an extendedversion of DCI format 2B and supports spatial multiplexing for up to 8layers.

DCI formats 3 and 3A may be used to complement the TPC informationincluded in the aforementioned DCI formats for uplink scheduling grantand downlink scheduling allocation, that is, to support semi-persistentscheduling. A 1-bit command is used per UE in the case of DCI format 3whereas a 2-bit command is used per UE in the case of DCI format 3A.

One of the above-mentioned DCI formats is transmitted through a PDCCH,and a plurality of PDCCHs may be transmitted in a control region. A UEcan monitor the plurality of PDCCHs.

PDCCH Processing

When DCI is transmitted on a PDCCH, a cyclic redundancy check (CRC) isadded to the DCI. The CRC is masked by a radio network temporaryidentifier (RNTI). Here, different RNTIs may be used according totransmission purpose of the DCI. Specifically, P-RNTI may be used for apaging message relating to network initiated connection establishment,RA-RNTI may be used in a case relating to random access, and SI-RNTI maybe used in a case relating to a symbol information block (SIB). In thecase of unicast transmission, C-RNTI, a unique UE identifier, may beused. The DCI with the CRC added thereto is coded into a predeterminedcode, and then adjusted to correspond to the quantity of resources usedfor transmission through rate-matching.

In PDCCH transmission, control channel elements (CCEs), contiguouslogical allocation units, are used to map a PDCCH to REs for efficientprocessing. A CCE includes 36 REs corresponding to 9 resource elementgroups (REGs). The number of CCEs necessary for a specific PDCCH dependson a DCI payload corresponding to a control information size, a cellbandwidth, a channel coding rate, etc. Specifically, the number of CCEsfor a specific PDCCH can be defined according to PDCCH format, as shownin Table 1.

TABLE 1 PDCCH Number of Number of Number of format CCEs REGs PDCCH bits0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

As shown in Table 1, the number of CCEs depends on the PDCCH format. Forexample, a transmitter can adaptively use PDCCH formats in such a mannerthat it uses PDCCH format 0 and changes PDCCH format 0 to PDCCH format 2when a channel status becomes poor.

Blind Decoding

While one of the above-mentioned PDCCH formats may be used, this is notsignaled to a UE. Accordingly, the UE performs decoding without knowingthe PDCCH format, which is referred to as blind decoding. Sinceoperation overhead is generated if a UE decodes all CCEs that can beused for downlink for each PDCCH, a search space is defined inconsideration of limitation for a scheduler and the number of decodingattempts.

The search space is a set of candidate PDCCHs composed of CCEs on whicha UE needs to attempt to perform decoding at an aggregation level. Theaggregation level and the number of candidate PDCCHs can be defined asshown in Table 2.

TABLE 2 The number Search space of PDCCH Aggregation level Size (CCEunit) candidates UE-specific 1 6 6 2 12 6 4 8 2 8 16 2 Common 4 16 4 816 2

As shown Table 2, the UE has a plurality of search spaces at eachaggregation level because 4 aggregation levels are present.

The search spaces may be divided into a UE-specific search space and acommon search space, as shown in Table 2. The UE-specific search spaceis for a specific UE. Each UE may check an RNTI and CRC which mask aPDCCH by monitoring a UE-specific search space thereof (attempting todecode a PDCCH candidate set according to an available DCI format) andacquire control information when the RNTI and CRC are valid.

The common search space is used for a case in which a plurality of UEsor all UEs need to receive PDCCHs, for system information dynamicscheduling or paging messages, for example. The common search space maybe used for a specific UE for resource management. Furthermore, thecommon search space may overlap with the UE-specific search space.

FIG. 4 illustrates an uplink subframe structure. An uplink subframe maybe divided into a control region and a data region in the frequencydomain. A physical uplink control channel (PUCCH) carrying uplinkcontrol information is allocated to the control region and a physicaluplink shared channel (PUSCH) carrying user data is allocated to thedata region. To maintain a single carrier property, a UE does nottransmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UE isallocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. Thus it is said that the RB pairallocated to the PUCCH is frequency-hopped over a slot boundary.

Physical Uplink Control Channel (PUCCH)

Uplink control information (UCI) transmitted on a PUCCH may include ascheduling request (SR), HARQ ACK/NACK information, and downlink channelmeasurement information.

The HARQ ACK/NACK information may be generated according to whether adownlink data packet on a PDSCH is successfully decoded. In conventionalwireless communication systems, 1 bit is transmitted as ACK/NACKinformation for downlink single codeword transmission and 2 bits aretransmitted as the ACK/NACK information for 2-codeword downlinktransmission.

The channel measurement information represents feedback informationabout a multiple input multiple output (MIMO) scheme and may include achannel quality indicator (CQI), a precoding matrix index (PMI), and arank indicator (RI) which may be collectively referred to as a CQI. 20bits per subframe may be used to transmit the CQI.

A PUCCH can be modulated using binary phase shift keying (BPSK) andquadrature phase shift keying (QPSK). Control information of a pluralityof UEs can be transmitted through a PUCCH. When code divisionmultiplexing (CDM) is performed in order to distinguish signals of theUEs from one another, a length-12 constant amplitude zeroautocorrelation (CAZAC) sequence is used. The CAZAC sequence is suitableto increase coverage by reducing a peak-to-average power ratio (PAPR) ofa UE or cubic metric (CM) because it maintains a specific amplitude inthe time domain and the frequency domain. ACK/NACK information withrespect to downlink data transmitted through a PUCCH is covered using anorthogonal sequence or an orthogonal cover (OC).

Control information signals transmitted on a PUCCH may be distinguishedusing cyclically shifted sequences having different cyclic shift (CS)values. A cyclically shifted sequence may be generated by cyclicallyshifting a base sequence by a specific CS amount. The specific CS amountis indicated by a CS index. The number of available CSs may varyaccording to channel delay spread. Various types of sequences may beused as the base sequence and the aforementioned CAZAC sequence is anexample of the various sequences.

The amount of control information that can be transmitted by a UEthrough a subframe can be determined according to the number of SC-FDMAsymbols (i.e. SC-FDMA symbols other than SC-FDMA symbols used forreference signal (RS) transmission for detection of coherent of a PUCCH)which can be used for control information transmission.

PUCCH format 1 is used to transmit an SR only. When the SR is solelytransmitted, an unmodulated waveform is applied, which will be describedin detail below.

PUCCH format 1a or 1b is used for HARQ ACK/NACK transmission. When HARQACK/NACK alone is transmitted in a subframe, PUCCH format 1a or 1b maybe used. Furthermore, HARQ ACK/NACK and SR may be transmitted in thesame subframe using PUCCH format 1a or 1b.

PUCCH format 2 is used for CQI transmission whereas PUCCH format 2a or2b is used for transmission of CQI and HARQ ACK/NACK. In the extended CPcase, PUCCH format 2 may be used for transmission of CQI and HARQACK/NACK.

FIG. 5 illustrates mapping of PUCCH formats to PUCCH regions in uplinkphysical resource blocks. In FIG. 5, N_(RB) ^(UL) denotes the number ofresource blocks on uplink and 0, 1, . . . , N_(RB) ^(UL)−1 denotephysical resource block numbers. PUCCHs are mapped to both edges ofuplink frequency blocks basically. PUCCH formats 2/2a/2b are mapped toPUCCH regions indicated by m=0,1, which represents that PUCCH formats2/2a/2b are mapped to resource blocks located at band-edges. PUCCHformats 2/2a/2b and PUCCH formats 1/1a/1b may be mixed and mapped toPUCCH regions indicated by m=2. PUCCH formats 1/1a/1b may be mapped toPUCCH regions indicated by m=3, 4, 5. The number N_(RB) ⁽²⁾ of PUCCH RBscan be used by PUCCH formats 2/2a/2b may be signaled to UEs in a cellthrough broadcast signaling.

Reference Signal (RS)

In a wireless communication system, a packet is transmitted on a radiochannel. In view of the nature of the radio channel, the packet may bedistorted during transmission. To receive the signal successfully, areceiver should compensate for distortion in the received signal usingchannel information. Generally, to enable the receiver to acquire thechannel information, a transmitter transmits a signal known to both thetransmitter and the receiver and the receiver acquires knowledge ofchannel information based on the distortion of the signal received onthe radio channel. This signal is called a pilot signal or an RS.

In case of data transmission and reception through multiple antennas,knowledge of channel states between transmit antennas and receiveantennas is required for successful signal reception. Accordingly, an RSshould exist separately for each transmit antenna.

Downlink RSs include a common reference signal (CRS) shared by all UEsin a cell and a dedicated RS (DRS) for a specific UE only. Informationfor channel estimation and demodulation may be provided using these RSs.

A receiver (UE) may estimate a channel state from a CRS and feed back anindicator relating to channel quality, such as a CQI, PMI and/or RI to atransmitter (eNB). The CRS may also be called a cell-specific RS. An RSrelating to feedback of channel state information (CSI) such asCQI/PMI/RI may be separately defined as a CSI-RS.

The DRS may be transmitted through a corresponding RE when data on aPDSCH needs to be demodulated. A higher layer may signal presence orabsence of the DRS to a UE. In addition, it is possible to signal thatthe DRS is valid only when a corresponding PDSCH is mapped to the UE.The DRS may also be referred to as a UE-specific RS or a demodulation RS(DMRS).

FIG. 6 illustrates patterns of mapping CRSs and DRSs defined in a 3GPPLTE system (e.g. release-8) to downlink RB pairs. A downlink RB pair asan RS mapping unit may be represented as (one subframe in the timedomain)×(12 subcarriers in the frequency domain). That is, a RB pair hasa length corresponding to 14 OFDM symbols in the time domain in thenormal CP case (FIG. 6(a)) and has a length corresponding to 12 OFDMsymbols in the extended CP case (FIG. 6(b)).

Sounding Reference Signal (SRS)

An SRS is used for an eNB to measure channel quality and perform uplinkfrequency-selective scheduling based on the channel quality measurement.The SRS is not associated with data and/or control informationtransmission. However, the usages of the SRS are not limited thereto.The SRS may also be used for enhanced power control or for supportingvarious start-up functions of non-scheduled UEs. The start-up functionsmay include, for example, an initial modulation and coding scheme (MCS),initial power control for data transmission, timing advance, andfrequency non-selective scheduling (in which a transmitter selectivelyallocates a frequency resource to the first slot of a subframe and thenpseudo-randomly hops to another frequency resource in the second slot ofthe subframe). The SRS may be used for measuring downlink channelquality on the assumption of the reciprocity of a radio channel betweenthe downlink and the uplink. This assumption is valid especially in atime division duplex (TDD) system in which downlink and uplink share thesame frequency band and are distinguished by time.

A subframe in which a UE within a cell is supposed to transmit an SRS isindicated by cell-specific broadcast signaling. A 4-bit cell-specificparameter ‘srsSubframeConfiguration’ indicates 15 possibleconfigurations for subframes carrying SRSs in each radio frame. Theseconfigurations may provide flexibility with which SRS overhead can beadjusted according to network deployment scenarios. The otherconfiguration (a 16^(th) configuration) represented by the parameter isfor switch-off of SRS transmission in a cell, suitable for a cellserving high-speed UEs, for example.

An SRS is always transmitted in the last SC-FDMA symbol of a configuredsubframe. Therefore, an SRS and a DMRS are positioned in differentSC-FDMA symbols. PUSCH data transmission is not allowed in an SC-FDMAsymbol designated for SRS transmission. Accordingly, even the highestsounding overhead (in the case where SRS symbols exist in all subframes)does not exceed 7%.

Each SRS symbol is generated for a given time unit and frequency band,using a base sequence (a random sequence or Zadoff-Chu (ZC)-basedsequence set), and all UEs within a cell use the same base sequence. SRStransmissions in the same time unit and the same frequency band from aplurality of UEs within a cell are distinguished orthogonally bydifferent cyclic shifts of the base sequence allocated to the pluralityof UEs. Although the SRS sequences of different cells may bedistinguished by allocating different base sequences to the cells,orthogonality is not ensured between the different base sequences.

Carrier Aggregation

FIG. 7 is a diagram illustrating carrier aggregation (CA). The conceptof a cell, which is introduced to manage radio resources in LTE-A isdescribed prior to the CA. A cell may be regarded as a combination ofdownlink resources and uplink resources. The uplink resources are notessential elements, and thus the cell may be composed of the downlinkresources only or both the downlink resources and uplink resources. Thisis defined in LTE-A release 10, and the cell may be composed of theuplink resources only. The downlink resources may be referred to asdownlink component carriers and the uplink resources may be referred toas uplink component carriers. A DL CC and a UL CC may be represented bycarrier frequencies. A carrier frequency means a center frequency in acell.

Cells may be divided into a primary cell (PCell) operating at a primaryfrequency and a secondary cell (SCell) operating at a secondaryfrequency. The PCell and Scell may be collectively referred to asserving cells. The PCell may be designated during an initial connectionestablishment, connection re-establishment or handover procedure of aUE. That is, the PCell may be regarded as a main cell relating tocontrol in a CA environment. A UE may be allocated a PUCCH and transmitthe PUCCH in the PCell thereof. The SCell may be configured after radioresource control (RRC) connection establishment and used to provideadditional radio resources. Serving cells other than the PCell in a CAenvironment may be regarded as SCells. For a UE in an RRC_connectedstate for which CA is not established or a UE that does not support CA,only one serving cell composed of the PCell is present. For a UE in theRRC-connected state for which CA is established, one or more servingcells are present and the serving cells include a PCell and SCells. Fora UE that supports CA, a network may configure one or more SCells inaddition to a PCell initially configured during connection establishmentafter initial security activation is initiated.

CA is described with reference to FIG. 7. CA is a technology introducedto use, a wider band to meet demands for a high transmission rate. CAcan be defined as aggregation of two or more component carriers (CCs)having different carrier frequencies. FIG. 7(a) shows a subframe when aconventional LTE system uses a single CC and FIG. 7(b) shows a subframewhen CA is used. In FIG. 8(b), 3 CCs each having 20 MHz are used tosupport a bandwidth of 60 MHz. The CCs may be contiguous ornon-contiguous.

A UE may simultaneously receive and monitor downlink data through aplurality of DL CCs. Linkage between a DL CC and a UL CC may beindicated by system information. DL CC/UL CC linkage may be fixed to asystem or semi-statically configured. Even when a system bandwidth isconfigured of N CCs, a frequency bandwidth that can bemonitored/received by a specific UE may be limited to M (<N) CCs.Various parameters for CA may be configured cell-specifically, UEgroup-specifically, or UE-specifically.

FIG. 8 is a diagram illustrating cross-carrier scheduling. Cross carrierscheduling is a scheme by which a control region of one of DL CCs of aplurality of serving cells includes downlink scheduling allocationinformation the other DL CCs or a scheme by which a control region ofone of DL CCs of a plurality of serving cells includes uplink schedulinggrant information about a plurality of UL CCs linked with the DL CC.

A carrier indicator field (CIF) is described first.

The CIF may be included in a DCI format transmitted through a PDCCH ornot. When the CIF is included in the DCI format, this represents thatcross carrier scheduling is applied. When cross carrier scheduling isnot applied, downlink scheduling allocation information is valid on a DLCC currently carrying the downlink scheduling allocation information.Uplink scheduling grant is valid on a UL CC linked with a DL CC carryingdownlink scheduling allocation information.

When cross carrier scheduling is applied, the CIF indicates a CCassociated with downlink scheduling allocation information transmittedon a DL CC through a PDCCH. For example, referring to FIG. 8, downlinkallocation information for DL CC B and DL CC C, that is, informationabout PDSCH resources is transmitted through a PDCCH in a control regionof DL CC A. A UE can recognize PDSCH resource regions and thecorresponding CCs through the CIF by monitoring DL CC A.

Whether or not the CIF is included in a PDCCH may be semi-statically setand UE-specifically enabled according to higher layer signaling. Whenthe CIF is disabled, a PDCCH on a specific DL CC may allocate a PDSCHresource on the same DL CC and assign a PUSCH resource on a UL CC linkedwith the specific DL CC. In this case, the same coding scheme, CCE basedresource mapping and DCI formats as those used for the conventionalPDCCH structure are applicable.

When the CIF is enabled, a PDCCH on a specific DL CC may allocate aPDSCH/PUSCH resource on a DL/UL CC indicated by the CIF from amongaggregated CCs. In this case, the CIF can be additionally defined inexisting PDCCH DCI formats. The CIF may be defined as a field having afixed length of 3 bits, or a CIF position may be fixed irrespective ofDCI format size. In this case, the same coding scheme, CCE basedresource mapping and DCI formats as those used for the conventionalPDCCH structure are applicable.

Even when the CIF is present, an eNB can allocate a DL CC set throughwhich a PDCCH is monitored. Accordingly, blinding decoding overhead of aUE can be reduced. A PDCCH monitoring CC set is part of aggregated DLCCs and a UE can perform PDCCH detection/decoding in the CC set only.That is, the eNB can transmit the PDCCH only on the PDCCH monitoring CCset in order to schedule a PDSCH/PUSCH for the UE. The PDCCH monitoringDL CC set may be configured UE-specifically, UE group-specifically orcell-specifically. For example, when 3 DL CCs are aggregated as shown inFIG. 8, DL CC A can be configured as a PDCCH monitoring DL CC. When theCIF is disabled, a PDCCH on each DL CC can schedule only the PDSCH on DLCC A. When the CIF is enabled, the PDCCH on DL CC A can schedule PDSCHsin other DL CCs as well as the PDSCH in DL CC A. When DL CC A is set asa PDCCH monitoring CC, DL CC B and DL CC C do not transmit PDSCHs.

In a system to which the aforementioned CA is applied, a UE can receivea plurality of PDSCHs through a plurality of downlink carriers. In thiscase, the UE should transmit ACK/NACK for data on a UL CC in a subframe.When a plurality of ACK/NACK signals is transmitted in a subframe usingPUCCH format 1a/1b, high transmit power is needed, a PAPR of uplinktransmission increases and a transmission distance of the UE from theeNB may decrease due to inefficient use of a transmit power amplifier.To transmit a plurality of ACK/NACK signals through a PUCCH, ACK/NACKbundling or ACK/NACK multiplexing may be employed.

There may be generated a case in which ACK/NACK information for a largeamount of downlink data according to application of CA and/or a largeamount of downlink data transmitted in a plurality of DL subframes in aTDD system needs to be transmitted through a PUCCH in a subframe. Inthis case, the ACK/NACK information cannot be successfully transmittedusing the above-mentioned ACK/NACK bundling or multiplexing when thenumber of ACK/NACK bits to be transmitted is greater than the number ofACK/NACK bits that can be supported by ACK/NACK bundling ormultiplexing.

ACK/NACK Multiplexing Scheme

In case of ACK/NACK multiplexing, contents of ACK/NACK for a pluralityof data units may be identified by combinations of ACK/NACK units usedfor actual ACK/NACK transmission and symbols modulated through QPSK. Forexample, if one ACK/NACK unit carries 2-bit information, a maximum of 2data units are received, and HARQ ACK for each received data unit isrepresented by one ACK/NACK bit, a transmitter transmitting the data canrecognize ACK/NACK results as shown in Table 3.

TABLE 3 HARQ-ACK(0), HARQ-ACK(1) n_(PUCCH) ⁽¹⁾ b(0), b(1) ACK, ACKn_(PUCCH, 1) ⁽¹⁾ 1, 1 ACK, NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 0, 1 NACK/DTX, ACKn_(PUCCH, 1) ⁽¹⁾ 0, 0 NACK/DTX, NACK n_(PUCCH, 1) ⁽¹⁾ 1, 0 NACK, DTXn_(PUCCH, 0) ⁽¹⁾ 1, 0 DTX, DTX N/A N/A

In Table 3, HARQ-ACK(i) (i=0, 1) denotes an ACK/NACK result for dataunit i. Since it is assumed that a maximum of 2 data units (data unit 0and data unit 1) are received, an ACK/NACK result for data unit 0 isrepresented as HARQ-ACK(0) and an ACK/NACK result for data unit 1 isrepresented as HARQ-ACK(1). DTX (discontinuous transmission) representsthat the data unit corresponding to HARQ-ACK(i) is not transmitted or areceiver cannot detect the data unit corresponding to HARQ-ACK(i).n_(PUCCH,X) ⁽¹⁾ denotes an ACK/NACK unit used for actual ACK/NACKtransmission. If a maximum of 2 ACK/NACK units are present, theseACK/NACK units can be represented as n_(PUCCH,0) ⁽¹⁾ and n_(PUCCH,1)⁽¹⁾. In addition, b(0), b(1) denotes 2 bits transmitted through aselected ACK/NACK unit. Modulation symbols transmitted through anACK/NACK unit are determined according to b(0),b(1)

For example, if the receiver successfully receive and decode 2 dataunits (i.e. in the case of ‘ACK,ACK’ in Table 3), the receiver transmits2 bits (1, 1) using ACK/NACK unit n_(PUCCH,1) ⁽¹⁾. When the receiverreceives 2 data units, if the receiver fails to decode a first data unit(e.g. data unit 0 corresponding to HARQ-ACK(0)) and successfully decodesa second data unit (e.g. data unit 1 corresponding to HARQ-ARK(1)) (i.e.in the case of ‘NACK/DTX, ACK’ in Table 3), the receiver transmits 2bits (0, 0) using ACK/NACK unit n_(PUCCH,1) ⁽¹⁾.

As described above, it is possible to transmit ACK/NACK information fora plurality of data units using a single ACK/NACK unit by mapping acombination of selection of an ACK/NACK unit and bits of an actuallytransmitted ACK/NACK unit (i.e. a combination of selection of one ofn_(PUCCH,0) ⁽¹⁾ and n_(PUCCH,1) ⁽¹⁾ in Table 3 and b(0),b(1)). ACK/NACKmultiplexing for two or more data units can be easily implemented byextending the aforementioned ACK/NACK multiplexing principle.

In this ACK/NACK multiplexing scheme, when at least one ACK is presentfor every data unit, NACK and DTX may not be distinguished from eachother (i.e. NACK and DTX may be coupled, as represented as NACK/DTX inTable 3). This is because all ACK/NACK states (i.e. ACK/NACK hypotheses)that can be generated when NACK and DTX are represented in adistinguished manner cannot be represented by only combinations ofACK/NACK units and QPSK-modulated symbols. When ACK is not present forany data unit (i.e. only NACK or DTX is present for all data units), itis possible to define one definite NACK that represents that only one ofACK/NACK results HARQ-ACK(i) corresponds to definite NACK (i.e. NACKdistinguished from DTX). In this case, an ACK/NACK unit for a data unitcorresponding to one definite NACK may be reserved in order to transmita plurality of ACK/NACK signals.

Semi-Persistent Scheduling (SPS)

DL/UL SPS signals which subframe (subframe period and offset) is usedfor a UE to perform SPS transmission/reception to the UE through radioresource control (RRC) signaling, and then performs actual SPSactivation and release through a PDCCH. That is, the UE performs SPSupon receiving the PDCCH that signals activation (or reactivation) (i.e.upon receiving a PDCCH from which SPS C-RNTI is detected) rather thanperforming SPS TX/RX right after being allocated SPS through RRCsignaling. Specifically, upon reception of an SPS activation PDCCH, theUE may assign a frequency resource according to RB allocation designatedby the PDCCH and start to perform TX/RX using a subframe period andoffset allocated thereto through RRC signaling by applying modulationand a coding rate according to MCS information to TX/RX. When the UEreceives a PDCCH that signals SPS release, the UE interrupts TX/RX.TX/RX interrupted in this manner may be resumed when the UE receives aPDCCH signaling activation (or reactivation) using a subframe period andoffset assigned through RRC signaling according to RB allocation and MCSdesignated by the PDCCH.

PDCCH formats defined in 3GPP LTE include DCI format 0 for uplink andDCI formats 1, 1A, 1B, 1C, 1D, 2, 2A, 3, 3A, etc. for downlink. Controlinformation such as a hopping flag, RB allocation, MCS (modulationcoding scheme), RV (redundancy version), NDI (new data indicator), TPC(transmit power control), cyclic shift DMRS (demodulation referencesignal), UL index, CQI (channel quality information) request, DLassignment index, HARQ process number, TPMI (transmitted precodingmatrix indicator), PMI (precoding matrix indicator) confirmation, etc.is selected, combined and transmitted for purposes of the formats.

More specifically, when a PDCCH is used for SPS activation/release, thismay validate that CRC of DCI transmitted on the PDCCH is masked with SPSC-RNTI and NDI is set to 0. In the case of SPS activation, a combinationof bit fields is set to 0 and used as a virtual CRC, as shown in Table4.

TABLE 4 DCI DCI DCI format 0 format 1/1A format 2/2A/2B TPC command forset to ‘00’ N/A N/A scheduled PUSCH Cyclic shift set to ‘000’ N/A N/ADMRS Modulation and MSB is set N/A N/A coding scheme to ‘0’ andredundancy version HARQ process N/A FDD: set FDD: set number to ‘000’ to‘000’ TDD: set TDD: set to ‘0000’ to ‘0000’ Modulation and N/A MSB isset For the enabled coding scheme to ‘0’ transport block: MSB is set to‘0’ Redundancy N/A set to ‘00’ For the enabled version transport block:set to ‘00’

The virtual CRC has additional error detection capability by checkingwhether a corresponding bit field value is an appointed value when anerror that cannot be checked even with a CRC is generated. When aspecific UE cannot detect an error generated in DCI allocated to anotherUE and mis-recognizes the error as SPS activation thereof, the one-timeerror generates continuous problems because the specific UT continuouslyuses the corresponding resource. Accordingly, wrong detection of SPS isprevented using the virtual CRC.

In the case of SPS release, a bit field value is set as shown in Table 5and used as a virtual CRC.

TABLE 5 DCI format 0 DCI format 1A TPC command for scheduled set to ‘00’N/A PUSCH Cyclic shift DMRS set to ‘000’ N/A Modulation and codingscheme and set to ‘11111’ N/A redundancy version Resource blockassignment and Set to all ‘1’s N/A hopping resource allocation HARQprocess number N/A FDD: set to ‘000’ TDD: set to ‘0000’ Modulation andcoding scheme N/A set to ‘11111’ Redundancy version N/A set to ‘00’Resource block assignment N/A set to all ‘1’s

Heterogeneous Deployment

FIG. 9 illustrates a heterogeneous network wireless communication systemincluding a macro eNB (MeNB) and micro eNBs (PeNB or FeNB). The term‘heterogeneous network’ means a network in which an MeNB and a PeNB orFeNB coexist even when they use the same radio access technology (RAT).

The MeNB is a normal eNB of a wireless communication system having widecoverage and high transmit power. The MeNB may be referred to as a macrocell.

The PeNB or FeNB may be referred to as a micro cell, pico cell, femtocell, home eNB (HeNB), relay, etc. (the exemplified PeNB or FeNB andMeNB may be collectively referred to as transmission points). The PeNBor FeNB, a micro version of the MeNB, can independently operate whileperforming most functions of the MeNB. The PeNB or FeNB is a non-overlaytype eNB that may be overlaid in an area covered by the MeNB or in ashadow area that is not covered by the MeNB. The PeNB or FeNB may covera smaller number of UEs while having a narrower coverage and lowertransmit power compared to the MeNB.

A UE (referred to as a macro-UE (MUE) hereinafter) may be directlyserved by the MeNB or a UE (referred to as a micro-UE (PUE or FUE)hereinafter) may be served by the PeNB or FeNB. In some cases, a PUEpresent in the coverage of the MeNB may be served by the MeNB.

The PeNB or FeNB may be classified into two types according to whetherUE access is limited.

The first type is an open access subscriber group (OSG) or non-closedaccess subscriber group (CSG) eNB and corresponds to a cell that allowsaccess of the existing MUE or a PUE of a different PeNB. The existingMUE can handover to the OSG type eNB.

The second type is a CSG eNB which does not allow access of the existingMUE or a PUE of a different PeNB. Accordingly, handover to the CSG eNBis impossible.

Inter-Cell Interference Control (ICIC)

In the heterogeneous network environment as described above,interference between neighboring cells may be a problem. To solve thisinter-cell interference, inter-cell interference control (ICIC) may beapplied. Conventional ICIC can be applied to frequency resources or timeresources.

As exemplary ICIC for the frequency resources, 3GPP LTE release-8defines a scheme of dividing a given frequency region (e.g. systembandwidth) into one or more sub-regions (e.g. physical resource blocks(PRBs)) and exchanging an ICIC message for each sub-region betweencells. For example, relative narrowband transmission power (RNTP)associated with downlink transmission power, UL interference overheadindication (IOI) and UL high interference indication (HII) associatedwith uplink interference are defined as information included in the ICICmessage for the frequency resources.

The RNTP is information indicating downlink transmission power used by acell that transmits an ICIC message in a specific frequency sub-region.For example, when an RNTP field for a specific frequency sub-region isset to a first value (e.g. 0), this represents that downlinktransmission power of a corresponding cell does not exceed a thresholdvalue in the specific frequency sub-region. When the RNTP field for thespecific frequency sub-region is set to a second value (e.g. 1), thisrepresents that the corresponding cell cannot guarantee the downlinktransmission power in the specific frequency sub-region. In other words,the downlink transmission power of the cell can be regarded as low whenthe RNTP field is 0, whereas the downlink transmission power of the cellcannot be regarded as low when the RNTP field is 1.

The UL IOI is information indicating the quantity of uplink interferencethat a cell transmitting an ICIC message suffers in a specific frequencysub-region. For example, when an IOI field for a specific frequencysub-region is set to a value corresponding to a large amount ofinterference, this represents that a corresponding cell suffers stronguplink interference in the specific frequency sub-region. A cellreceiving an ICIC message can schedule UEs using low uplink transmissionpower from among UEs thereof in a frequency sub-region corresponding toIOI indicating strong uplink interference. Accordingly, UEs can performuplink transmission with low transmit power in the frequency sub-regioncorresponding to the IOI indicating strong uplink interference, and thusuplink interference that a neighboring cell (i.e. cell transmitting theICIC message) suffers can be alleviated.

The UL HII is information indicating a degree of interference (or uplinkinterference sensitivity) that may be generated for the correspondingfrequency sub-region according to uplink transmission in the celltransmitting the ICIC message. For example, when an HII field is set toa first value (e.g. 1) for a specific frequency sub-region, thisrepresents that the cell transmitting the ICIC message may schedule UEshaving high uplink transmit power for the specific frequency sub-region.On the contrary, when the HII field is set to a second value (e.g. 0)for the specific frequency sub-region, this represents that the celltransmitting the ICIC message may schedule UEs having low uplinktransmission power for the specific frequency sub-region. The cellreceiving the ICIC message can avoid interference from the celltransmitting the ICIC message by preferentially scheduling UEs to thefrequency sub-region to which the HII field is set to the second value(e.g. 0) and scheduling UEs that can successfully operate even in astrong interference environment to the frequency sub-region to which theHII field is set to the first value (e.g. 1).

As exemplary ICIC for the time resources, 3GPP LTE-A (or 3GPP LTErelease-10) defines a scheme of dividing the entire time domain into oneor more time sub-regions (e.g. subframes) in the frequency domain andexchanging information on whether silencing is performed on each timesub-region between cells. The cell transmitting the ICIC message maytransmit information indicating that silencing is performed in aspecific subframe to neighboring cells and does not schedule a PDSCH ora PUSCH in the specific subframe. The cell receiving the ICIC messagemay schedule uplink and/or downlink transmission for UEs on the subframein which silencing is performed in the cell transmitting the ICICmessage.

Silencing may represent an operation in which a specific cell does nottransmit signals (or transmits zero power or weak power) in a specificsubframe on uplink and downlink. As an example of silencing, a specificcell can set a specific subframe as an almost blank subframe (ABS).There are two types of ABS. Specifically, one type is an ABS in a normalsubframe in which a data region is vacant while a CRS is transmitted andthe other type is an ABS in an MBSFN subframe in which even a CRS is nottransmitted. In the ABS in a normal subframe, interference of the CRSmay be present. Accordingly, the ABS in an MBSFN subframe has anadvantage in terms of interference. However, use of the ABS in an MBSFNsubframe is limited, and thus the two ABS may be used together.

FIG. 10 illustrates a scheme of alleviating interference by allocatingPDSCHs to UEs located at the edges of cells in orthogonal frequencyregions, which can be used to exchange scheduling information betweeneNBs. However, a PDCCH is transmitted over the entire downlinkbandwidth, as described above, and thus interference due to the PDCCHcannot be mitigated. For example, since a time-frequency region in whicha PDCCH is transmitted from eNB1 to UE1 and a time-frequency region inwhich a PDCCH is transmitted from eNB2 to UE2 overlap, PDCCHtransmission for UE1 and PDCCH transmission for UE2 interfere with eachother.

Referring to FIG. 11, a PUCCH or a PUSCH transmitted from UE1 mayinterfere with a PDCCH or a PDSCH received by UE2 adjacent to UE1. Here,if scheduling information is exchanged between eNB1 and eNB2,interference in the PDSCH can be avoided by allocating the UEs toorthogonal frequency regions. However, the PDCCH is affected by thePUCCH or PUSCH transmitted from UE1.

For this reason, introduction of an ePDCCH different from the PDCCH isdiscussed. The ePDCCH is introduced to effectively support CoMP(coordinated multipoint transmission), MU-MIMO (multiuser-multiple inputmultiple output) as well as to alleviate interference.

Even when the ePDCCH is introduced, it is impossible to avoidinterference applied to a PHICH on which ACK/NACK information for aPUSCH is transmitted. This interference may cause PUSCH retransmissionto deteriorate system performance. Furthermore, when the quantity ofresources transmitted on the PHICH increases, PDCCH capacity decreases,and thus PDCCH blocking probability decreases.

Methods of Generating a Sequence of ePHICH Modulation Symbols forCoherent Detection

Methods of generating a sequence of modulation symbols for an ePHICHaccording to embodiments of the present invention will now be described.A modulation symbol sequence described below may be mapped to one ormore layers, precoded, mapped to resource elements (REs) according to anembodiment of the present invention, and transmitted through a pluralityof antenna ports. While the modulation symbol sequence has a length of12 on the assumption that the number of REs for the ePHICH is 12 in thefollowing description, the present invention is not limited thereto andthe modulation symbol sequence can have various lengths.

A method of generating a modulation symbol sequence may be summarized asgeneration of a bit sequence according to a predetermined coding ratefrom reception acknowledgement for a transport block (TB) received froma UE through a PUSCH, that is, 1-bit ACK/NACK information, generation ofa block of complex-valued modulation symbols by modulating the generatedbit sequence, and then application of an orthogonal sequence to theblock of complex-valued modulation symbols.

The method of generating a modulation symbol sequence will be describedbelow as two operations of;

1) generating a bit sequence from ACK/NACK information and thengenerating a block of complex-valued modulation symbols, and

ii) applying an orthogonal sequence to the block of complex-valuedmodulation symbols.

First of all, the operation of generating a bit sequence from ACK/NACKinformation and then generating a block of complex-valued modulationsymbols will now be described. ACK/NACK may be information with respectto one or more TBs. An operation of generating a block of complex-valuedmodulation symbols from ACK/NACK information for one TB is describedfirst, and then an operation of generating a block of complex-valuedmodulation symbols from ACK/NACK information for two TBs is described.

1-bit ACK/NACK information for one TB may be converted to a bit sequenceb(i) according to a predetermined coding rate and then transformed to ablock of complex-valued modulation symbols, z(i), through BPSK usingTables 6 and 7.

TABLE 6 b(i) I Q 0  1/{square root over (2)}  1/{square root over (2)} 1−1/{square root over (2)} −1/{square root over (2)}

TABLE 7 b(i) z(i) 0 1 1 −1

For example, when the 1-bit ACK/NACK information is 1, a 12-bit sequenceb(i)=1, i=0, . . . , M_(bit)−1, M_(bit)=12, which is generated byrepeating the ACK/NACK information twelve times according to a codingrate of 1/12, can be modulated using BPSK according to Table 7 togenerate a block of complex-valued modulation symbols, z(i)=−1, i=0,M_(S)−1, M_(S)=12.

When the ACK/NACK information corresponds to 1, a 3-bit sequence b(i)=1,i=0, . . . , M_(bit)=3, which is generated by repeating the ACK/NACKinformation three times according to a coding rate of ⅓, may be mappedaccording to Table 7 to generate a block of complex-valued modulationsymbols, z(i)=−1, i=0, M_(S)=1, M_(S)=3.

If a coding rate of 1 is used, that is, when the ACK/NACK information isnot repeated, a block of complex-valued modulation symbols, b(i)=1, i=0,M_(bit)−1, M_(bit)=1 can be generated from a 1-bit sequence b(i)=1, i=0,. . . , M_(bit)−1, M_(bit)=1 using Table 7.

The operation of generating a block of complex-valued modulation symbolsfrom 2-bit ACK/NACK information for 2 TBs will now be described withreference to FIG. 12. In description associated with FIG. 12, 2 TBs maybe transmitted on a PUSCH from a UE. Specifically, the UE may map the 2TBs to 2 to 4 layers, precode the mapped TBs, and then transmit theprecoded TBs through a plurality of antennas. Otherwise, the 2 TBs maybe TBs respectively transmitted through PUSCHs from 2 UEs each using oneTB.

FIG. 12(a) illustrates a method of generating a 24-bit sequenceaccording to a coding rate of 1/12 from 2-bit ACK/NACK information.Referring to FIG. 12(a), ACK/NACK information PUSCH TB#0 A/N and PUSCHTB#1 A/N for 2 TBs can be generated as the 24-bit sequence b(i)=1, i=0,. . . , M_(bit)−1, M_(bit)=24 according to the coding rate of 1/12.Here, the 24-bit sequence may be generated in various manners forrespective cases, as shown in the figure. A case in which PUSCH TB#0 A/Nis 1 and PUSCH TB#1 A/N is 0 is exemplified for convenience ofdescription.

$\begin{matrix}{{b(i)} = \{ {{{\begin{matrix}1 & {{{for}\mspace{14mu} i\;{mod}\; 2} = 0} \\0 & {{{for}\mspace{14mu} i\;{mod}\; 2} = 1}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 24}} } & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

Case 2 and Case 3 can be represented by the following equations 2 and 3.

$\begin{matrix}{{b(i)} = \{ {{{\begin{matrix}1 & {{{{for}\mspace{14mu} i\;{mod}\; 4} = 0},1} \\0 & {{{{for}\mspace{14mu} i\;{mod}\; 4} = 2},3}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 24}} } & \lbrack {{Equation}\mspace{14mu} 2} \rbrack \\{{b(i)} = \{ {{{\begin{matrix}1 & {{{{for}\mspace{14mu} i\;{mod}\; 8} = 0},1,2,3} \\0 & {{{{for}\mspace{14mu} i\;{mod}\; 8} = 4},5,6,7}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 24}} } & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

Case 4 and Case 5 can be represented by the following equations 4 and 5.

$\begin{matrix}{{b(i)} = \{ {{{\begin{matrix}1 & {{{for}\mspace{14mu}\lfloor {{i/M_{bit}}/2} \rfloor{mod}\; 2} = 0} \\0 & {{{for}\mspace{14mu}\lfloor {{i/M_{bit}}/2} \rfloor{mod}\; 2} = 1}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 24}} } & \lbrack {{Equation}\mspace{14mu} 4} \rbrack \\{{b(i)} = \{ {{{\begin{matrix}1 & {{{for}\mspace{14mu}\lfloor {{i/M_{bit}}/2} \rfloor} = 0} \\0 & {{{for}\mspace{14mu}\lfloor {{i/M_{bit}}/2} \rfloor} = 1}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 24}} } & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

The 24-bit sequence generated in this manner may be converted to a blockof complex-valued modulation symbols, z(i), i=0, . . . , M_(s)−1,M_(s)=12, using a QPSK modulation mapping table such as Table 8 or Table9.

TABLE 8 b(i), b(i + 1) I Q 00  1/{square root over (2)}  1/{square rootover (2)} 01  1/{square root over (2)} −1/{square root over (2)} 10−1/{square root over (2)}  1/{square root over (2)} 11 −1/{square rootover (2)} −1/{square root over (2)}

TABLE 9 b(i), b(i + 1) I Q 00 1 0 01 0 −1 10 0 1 11 −1 0

For example, when PUSCH TB#0 A/N is 1 and PUSCH TB#1 A/N is 0, in Case1, the block of complex-valued modulation symbols, modulated using Table9, can be represented by the following equation 6.z(i)=j, i=0, . . . , M _(s)−1, M _(s)=12  [Equation 6]

In Case 2 and Case 3, the block of complex-valued modulation symbols canbe represented by the following equations 7 and 8, respectively.

$\begin{matrix}{{z(i)} = \{ {{{\begin{matrix}{- 1} & {{{for}\mspace{14mu} i\;{mod}\; 2} = 0} \\1 & {{{for}\mspace{14mu} i\;{mod}\; 2} = 1}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 12}} } & \lbrack {{Equation}\mspace{14mu} 7} \rbrack \\{{z(i)} = \{ {{{\begin{matrix}{- 1} & {{{{for}\mspace{14mu} i\;{mod}\; 4} = 0},1} \\1 & {{{{for}\mspace{14mu} i\;{mod}\; 4} = 2},3}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 12}} } & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

In Case 4 and Case 5, the block of complex-valued modulation symbols canbe represented by the following equations 9 and 10, respectively.

$\begin{matrix}{{z(i)} = \{ {{{\begin{matrix}{- 1} & {{{for}\mspace{14mu}\lfloor {{i/M_{s}}/2} \rfloor{mod}\; 2} = 0} \\1 & {{{for}\mspace{14mu}\lfloor {{i/M_{s}}/2} \rfloor{mod}\; 2} = 1}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 12}} } & \lbrack {{Equation}\mspace{14mu} 9} \rbrack \\{{z(i)} = \{ {{{\begin{matrix}{- 1} & {{{for}\mspace{14mu}\lfloor {{i/M_{s}}/2} \rfloor} = 0} \\1 & {{{for}\mspace{14mu}\lfloor {{i/M_{s}}/2} \rfloor} = 1}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 12}} } & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

FIG. 12(b) illustrates a method of generating a 12-bit sequence from2-bit ACK/NACK information using a coding rate of ⅙. The 12-bit sequencemay be modulated through BPSK to generate a length-12 block ofcomplex-valued modulation symbols or modulated through QPSK to generatea length-6 block of complex-valued modulation symbols.

The following table 10 shows a method of generating a bit sequence andmodulating the bit sequence using BPSK or QPSK to generate a block ofcomplex-valued modulation symbols in Case 1, Case 2, Case 3 and Case 4as mathematical expressions on the assumption that PUSCH TB#0 A/N is 1,PUSCH TB#1 A/N is 0, BPSK uses Table 7, and QPSK uses Table 9.

TABLE 10 Generation of bit sequence Case 1 $\begin{matrix}{{b(i)} = \{ \begin{matrix}1 & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 0} \\0 & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 12}}\end{matrix}\quad$ case 2 $\;{\begin{matrix}{{b(i)} = \{ \begin{matrix}1 & {{{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 4} = 0},1} \\0 & {{{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 4} = 2},3}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 12}}\end{matrix}\quad}$ Case 3 $\begin{matrix}{{b(i)} = \{ \begin{matrix}1 & {{{for}\mspace{11mu}\lfloor {{i/M_{bit}}/4} \rfloor\;{mod}\mspace{11mu} 2} = 0} \\0 & {{{for}\mspace{11mu}\lfloor {{i/M_{bit}}/4} \rfloor\;{mod}\mspace{11mu} 2} = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 12}}\end{matrix}{\quad\quad}$ Case 4 $\begin{matrix}{{b(i)} = \{ \begin{matrix}1 & {{{for}\mspace{11mu}\lfloor {{i/M_{bit}}/2} \rfloor}\; = 0} \\0 & {{{for}\mspace{11mu}\lfloor {{i/M_{bit}}/2} \rfloor}\; = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 12}}\end{matrix}\quad$ Generation of block of modulation symbols case 1 BPSK$\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 0} \\1 & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 12}}\end{matrix}{\quad\quad}$ QPSK z(i) = j i = 0, . . . , M_(s) − 1, M_(s)= 6 case 2 BPSK $\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 4} = 0},1} \\1 & {{{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 4} = 2},3}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 12}}\end{matrix}\quad$ QPSK $\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 0},1} \\1 & {{{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 2},3}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 6}}\end{matrix}{\quad\quad}$ case 3 BPSK $\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{for}\mspace{11mu}\lfloor {{i/M_{bit}}/4} \rfloor\;{mod}\mspace{11mu} 2} = 0} \\1 & {{{for}\mspace{11mu}\lfloor {{i/M_{bit}}/4} \rfloor\;{mod}\mspace{11mu} 2} = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 12}}\end{matrix}\quad$ QPSK $\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 3} = 0} \\j & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 3} = 1} \\1 & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 3} = 2}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 6}}\end{matrix}\quad$ case 4 BPSK $\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{for}\mspace{11mu}\lfloor {{i/M_{s}}/2} \rfloor}\; = 0} \\1 & {{{for}\mspace{11mu}\lfloor {{i/M_{s}}/2} \rfloor}\; = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 12}}\end{matrix}\quad$ QPSK $\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{for}\mspace{11mu}\lfloor {{i/M_{s}}/2} \rfloor}\; = 0} \\1 & {{{for}\mspace{11mu}\lfloor {{i/M_{s}}/2} \rfloor}\; = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 6}}\end{matrix}\quad$

FIG. 12(c) illustrates a method of generating a 6-bit sequence from2-bit ACK/NACK information using a coding rate of ⅓. The 6-bit sequencemay be modulated through BPSK to generate a length-6 block ofcomplex-valued modulation symbols or modulated through QPSK to generatea length-3 block of complex-valued modulation symbols.

In this case, the bit sequence and the block of complex-valuedmodulation symbols generated using QPSK in Case 1 and Case 3 can berepresented as shown in Table 11. PUSCH TB#0 A/N is 1, PUSCH TB#1 A/N is0, BPSK uses Table 7, and QPSK uses Table 9.

TABLE 11 Generation of bit sequence case 1 $\begin{matrix}{{b(i)} = \{ \begin{matrix}1 & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 0} \\0 & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 6}}\end{matrix}\quad$ case 3 $\begin{matrix}{{b(i)} = \{ \begin{matrix}1 & {{{for}\mspace{11mu}\lfloor {{i/M_{bit}}/2} \rfloor}\; = 0} \\0 & {{{for}\mspace{11mu}\lfloor {{i/M_{bit}}/2} \rfloor}\; = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{bit} - 1},{M_{bit} = 6}}\end{matrix}\quad$ Generation of block of modulation symbols case 1 BPSK$\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 0} \\1 & {{{for}\mspace{14mu} i\mspace{11mu}{mod}\mspace{11mu} 2} = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 6}}\end{matrix}{\quad\quad}$ QPSK z(i) = j i = 0, . . . , M_(s) − 1, M_(s)= 3 case 3 BPSK $\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{for}\mspace{11mu}\lfloor {{i/M_{s}}/2} \rfloor}\; = 0} \\1 & {{{for}\mspace{11mu}\lfloor {{i/M_{s}}/2} \rfloor}\; = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 6}}\end{matrix}\quad$ QPSK $\begin{matrix}{{z(i)} = \{ \begin{matrix}{- 1} & {{{for}\mspace{11mu}\lfloor {{i/M_{s}}/2} \rfloor}\; = 0} \\1 & {{{for}\mspace{11mu}\lfloor {{i/M_{s}}/2} \rfloor}\; = 1}\end{matrix} } \\{{i = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 6}}\end{matrix}\quad$

Unlike the methods illustrated in FIG. 12, it is possible to generate ablock of complex-valued modulation symbols from 2-bit ACK/NACKinformation using a coding rate of 1, that is, without repeatingACK/NACK information bits.

For example, when PUSCH TB#0 A/N is 1, PUSCH TB#1 A/N is 0, if thesebits are respectively configured as a most significant bit (MSB) and aleast significant bit (LSB) and length-2 modulation symbols areconfigured, a bit sequence b(i), i=0, . . . , M_(bit)−1 having 2 bits(M_(bit)=2) can be represented by the following equation 11.

$\begin{matrix}{{b(i)} = \{ \begin{matrix}{1\mspace{14mu}( {T\; B\mspace{14mu}{\# 0}\mspace{14mu} A\text{/}N} )} & {{{for}\mspace{14mu} i} = 0} \\{0\mspace{14mu}( {T\; B\mspace{14mu}{\# 1}\mspace{14mu} A\text{/}N} )} & {{{for}\mspace{14mu} i} = 1}\end{matrix} } & \lbrack {{Equation}\mspace{14mu} 11} \rbrack\end{matrix}$

By mapping the bit sequence using the modulation mapping table of Table7, a block of complex-valued modulation symbols, z(i), i=0, . . . ,M_(s)−1, M_(s)=2, can be generated. The block of complex-valuedmodulation symbols can be represented by the following equation 12.

$\begin{matrix}{{z(i)} = \{ {{{\begin{matrix}{- 1} & {{{for}\mspace{14mu} i} = 0} \\1 & {{{for}\mspace{14mu} i} = 1}\end{matrix}i} = 0},\ldots\mspace{14mu},{M_{s} - 1},{M_{s} = 2}} } & \lbrack {{Equation}\mspace{14mu} 12} \rbrack\end{matrix}$

If the QPSK modulation mapping table of Table 9 is used, the block ofcomplex-valued modulation symbols can be represented by the followingequation 13.z(i)=ji=0, . . . , M _(s)−1, M _(s)−1  [Equation 13]

A description will be given of ii) the procedure of applying anorthogonal sequence to modulation symbol blocks in various lengths togenerate a modulation symbol sequence, which follows i) the procedure ofgenerating a bit sequence from ACK/NACK information and then generatinga block of complex-valued modulation symbols.

For reference, a modulation symbol sequence z(i) is identical to theblock of complex-valued modulation symbols, z(i), if the block ofcomplex-valued modulation symbols has a length of 12 (M_(s)=12) and theorthogonal sequence is not applied to the block of complex-valuedmodulation symbols.

In the following description, the orthogonal sequence may be a Walshcode (or Walsh-Hadamard code) or a DFT code. The Walsh code hasorthogonality and is mainly used to identify a channel of each CDMA UEbecause there is no correlation between codes. The Walsh code has aproperty that 0s (or −1s) and 1s are obtained when multiplication(Exclusive-OR) is performed on different code elements and the averageof 0s and 1s becomes 0. In addition, the number of bits of one typeequals the number of bits of the other type. The following table 12shows Walsh codes applicable to the embodiments of the presentinvention.

TABLE 12 Orthogonal sequence Sequence Normal cyclic Extended cyclicindex prefix prefix n_(PHICH) ^(seq) N_(SF) ^(PHICH) = 4 N_(SF) ^(PHICH)= 2 0 [+1 +1 +1 +1] [+1 +1] 1 [+1 −1 +1 −1] [+1 −1] 2 [+1 +1 −1 −1] [+j+j] 3 [+1 −1 −1 +1] [+j −j] 4 [+j +j +j +j] — 5 [+j −j +j −j] — 6 [+j +j−j −j] — 7 [+j −j −j +j] —

The DFT code also has orthogonality. A DFT matrix is a representation ofdiscrete Fourier transform (DFT) in the form of matrix multiplication.The DFT code can be generated using the DFT matrix. N-point DFT can berepresented as an N×N matrix multiplication such as X=Wx. Here, X is aninput signal and X is a signal obtained by performing DFT on the inputsignal. W having a size of N×N can be defined as

$W = {( \frac{\omega^{j\; k}}{\sqrt{N}} )_{j,{k = 0},\mspace{11mu}\ldots\mspace{14mu},{N - 1}}.}$This can be represented by the following equation 14.

$\begin{matrix}{W = {\frac{1}{\sqrt{N}}\begin{bmatrix}1 & 1 & 1 & 1 & \ldots & 1 \\1 & \omega & \omega^{2} & \omega^{3} & \ldots & \omega^{N - 1} \\1 & \omega^{2} & \omega^{4} & \omega^{6} & \ldots & \omega^{2{({N - 1})}} \\\vdots & \vdots & \vdots & \vdots & \; & \vdots \\1 & \omega^{N - 1} & \omega^{2{({N - 1})}} & \omega^{3{({N - 1})}} & \ldots & \omega^{{({N - 1})}{({N - 1})}}\end{bmatrix}}} & \lbrack {{Equation}\mspace{14mu} 14} \rbrack\end{matrix}$

ω is N-th primitive root of unity

${\mathbb{e}}^{\frac{2\pi\; i}{N}}$where i=√{square root over (−1)}. The following table 13 shows DFTsequences applicable to the embodiments of the present invention.

TABLE 13 Sequence index Normal cyclic Extended cyclic n _(oc) ⁽{tildeover (^(p))}⁾(n_(s)) prefix prefix 0 [1 1 1] [1 1] 1 [1 e^(j2π/3)e^(j4π/3)] [1 −1] 2 [1 e^(j4π/3) e^(j2π/3)] N/A

When the length of the block of complex-valued modulation symbols towhich the orthogonal sequence is applied is 12, a) spreading using theorthogonal sequence may not be applied. If the length of the block ofcomplex-valued modulation symbols is shorter than 12, b) a modulationsymbol sequence spread using the orthogonal sequence can be generated.Cases a) and b) will now be described.

a) Case in which Spreading Using the Orthogonal Sequence is notPerformed

The modulation symbol sequence d(i) can be generated by multiplying theblock of complex-valued modulation symbols, z(i), by an orthogonalsequence (Walsh code or DFT code). Specifically, the modulation symbolsequence can be generated by multiplying the block of complex-valuedmodulation symbols z(i), i=0, . . . , M_(s)−1 having a length ofM_(s)=12 by respective elements of an orthogonal sequence [w(0) . . .w(N^(PHICH)−1)] having a length of 4(N^(PHICH)=4) without spreading theblock of complex-valued modulation symbols (M_(sym)=M_(s)). Here, themodulation symbol sequence d(i), i=0, . . . , M_(sym)−1 can berepresented by the following equation 15.d(i)=w(i mod N ^(PHICH))·z(i), i=0, . . . , M _(sym)−1  [Equation 15]

FIG. 13(a) shows a length-12 modulation symbol sequence obtained usingthe orthogonal sequence having a normal cyclic prefix and a length of4(N^(PHICH)=4) and corresponding to sequence index #1 in Table 12. Theorthogonal sequence is repeated three times as shown in FIG. 13(b).

FIG. 13(b) shows a modulation symbol sequence generated using a length-3DFT code as the orthogonal sequence. Here, the orthogonal sequencecorresponding to sequence index #1 in Table 13 is repeated four times.

Different orthogonal sequence lengths or the same orthogonal sequencelength may be used for a normal cyclic prefix case and an extendedcyclic prefix case.

If the length of the orthogonal sequence equals the length of the blockof complex-valued modulation symbols, the modulation symbol sequence canbe generated by applying the orthogonal sequence to the block ofcomplex-valued modulation symbols without repeating the orthogonalsequence. Specifically, when a block of complex-valued modulationsymbols z(i), i=0, . . . , M_(s)−1 having a length of 12 is multipliedby an orthogonal sequence [w(0) . . . w(N^(PHICH)−1)] having a length of12 (N^(PHICH)12), a modulation symbol sequence represented by thefollowing equation 16 is generated.d(i)=w(i mod N ^(PHICH))·z(i), i=0, . . . , M _(sym)−1  [Equation 16]

Here, the length-12 orthogonal sequence may be selected from thefollowing tables 14 and 15.

TABLE 14 Sequence index Orthogonal sequence n_(PHICH) ^(seq) Normalcyclic prefix N^(PHICH) = 12 0 [+1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1] 1[+1 −1 +1 −1 +1 −1 +1 −1 +1 −1 +1 −1] 2 [+1 +1 +1 +1 +1 +1 −1 −1 −1 −1−1 −1] 3 [+j +j +j +j +j +j +j +j +j +j +j +j] 4 [+j −j +j −j +j −j +j−j +j −j +j −j] 5 [+j +j +j +j +j +j −j −j −j −j −j −j]

TABLE 15 Sequence Orthogonal sequence index Normal cyclic prefixn_(PHICH) ^(seq) N^(PHICH) = 12 0 [1 1 1 1 1 1 1 1 1 1 1 1] 1 [1e^(jπ/6) e^(jπ/3) e^(jπ/2) e^(j2π/3) e^(j5π/6) e^(jπ) e^(j7π/6)e^(j4π/3) e^(j3π/4) e^(j5π/3) e^(j11π/6)] 2 [1 e^(jπ/3) e^(j2π/3) e^(jπ)e^(j4π/3) e^(j5π/3) 1 e^(jπ/3) e^(j2π/3) e^(jπ) e^(j4π/3) e^(j5π/3)] 3[1 e^(jπ/2) e^(jπ) e^(j3π/4) 1 e^(jπ/2) e^(jπ) e^(j3π/4) 1 e^(jπ/2)e^(jπ) e^(j3π/4)] 4 [1 e^(j2π/3) e^(j4π/3) 1 e^(j2π/3) e^(j4π/3) 1e^(j2π/3) e^(j4π/3) 1 e^(j2π/3) e^(j4π/3)] 5 [1 e^(j5π/6) e^(j5π/3)e^(jπ/2) e^(j4π/3) e^(jπ/6) e^(j11π/6) e^(j2π/3) e^(j3π/4) e^(jπ/3)e^(j7π/6) 1] 6 [1 e^(jπ) 1 e^(jπ) 1 e^(jπ) 1 e^(jπ) 1 e^(jπ) 1 e^(jπ)] 7[1 e^(j7π/6) e^(jπ/3) e^(j4π/3) e^(jπ/2) e^(j5π/3) e^(j5π/6) 1 e^(j7π/6)e^(jπ/3) e^(j4π/3) e^(jπ/2)] 8 [1 e^(j4π/3) e^(j2π/3) 1 e^(j4π/3)e^(j2π/3) 1 e^(j4π/3) e^(j2π/3) 1 e^(j4π/3) e^(j2π/3)] 9 [1 e^(j3π/4)e^(jπ) e^(jπ/2) 1 e^(j3π/4) e^(jπ) e^(jπ/2) 1 e^(j3π/4) e^(jπ) e^(jπ/2)]10 [1 e^(j5π/3) e^(j4π/3) e^(jπ) e^(j2π/3) e^(jπ/3) 1 e^(j5π/3)e^(j4π/3) e^(jπ) e^(j2π/3) e^(jπ/3)] 11 [1 e^(j11π/6) e^(j5π/3)e^(j3π/4) e^(j4π/3) e^(j7π/6) e^(jπ) e^(j5π/6) e^(j2π/3) e^(jπ/2)e^(jπ/3) e^(jπ/6)]

FIG. 14(a) illustrates generation of a length-12 modulation symbolsequence using the orthogonal sequence corresponding to sequence index#1 in Table 14 and FIG. 14(b) illustrates generation of a modulationsymbol sequence using the orthogonal sequence corresponding to sequenceindex #1 in Table 15.

b) Case in which Spreading is Performed using the Orthogonal Sequence

A description will be given of a method of generating a modulationsymbol sequence spread using an orthogonal sequence when the length ofthe block of complex-valued modulation symbols is less than the number(e.g. 12) of REs for an ePHICH.

The modulation symbol sequence may be generated by applying anorthogonal sequence [w(0) . . . w(N^(PHICH)−1)] having a length of 4(N^(PHICH)=4) to a length-3 (M_(s)=3) block of complex-valued modulationsymbols z(i), i=0, . . . , M_(s)−1. Here, modulation symbol sequenced(i), i=0, . . . , M_(sym)−1 can be represented using the followingequation 17.d(i)=w(i mod N ^(PHICH))·z(└i/N ^(PHICH)┘), i=0, . . . , M_(sym)−1  [Equation 17]

That is, the method of generating a modulation symbol sequence throughspreading using an orthogonal sequence can be performed in such a mannerthat the respective symbols of the block of complex-valued modulationsymbols are sequentially multiplied by the orthogonal sequence, as inEquation 17.

Alternatively, when the length of the block of complex-valued modulationsymbols is 4, a length-3 orthogonal sequence may be used.

FIG. 15(a) illustrates a scheme of generating a length-12 modulationsymbol sequence using the orthogonal sequence having a normal cyclicprefix and a length of 4(N^(PHICH)=4) and corresponding to sequenceindex #1, shown in Table 12. That is, symbols 0, 1 and 2 of a block ofcomplex-valued modulation symbols can be sequentially multiplied by theorthogonal sequence to generate the modulation symbol sequence.

FIG. 15(b) illustrates a scheme of generating a modulation symbolsequence using the orthogonal sequence corresponding to sequence index#1 shown in Table 14. Specifically, a modulation symbol sequence d(i),i=0, . . . , M_(sym)−1 can be generated by sequentially multiplying eachsymbol of a block of complex-valued modulation symbols z(i) by elementsof an orthogonal sequence w(i mod N^(PHICH)).

When the orthogonal sequence is used to generate a modulation symbolsequence, as described above, the orthogonal sequence may be allocatedUE specifically, TB specifically, or UE-and-TB specifically.

Different orthogonal sequences may be respectively allocated to UEs suchthat the same resource can be simultaneously used by the UEs. Forexample, if sequence index #0 is allocated to UE #0 and sequence index#1 is allocated to UE #1, PUSCH ACK/NACK information of UE #0 and PUSCHACK/NACK information of UE #1 can be simultaneously transmitted usingthe same resource. When UE multiplexing is employed in this manner,PUSCH ACK/NACK of many UEs can be simultaneously transmitted using asmall amount of resources.

For a UE, different orthogonal sequences may be respectively allocatedto 2 TBs to simultaneously transmit ACK/NACK information correspondingto 2 TBs using the same resource when a maximum number of TBs that canbe transmitted by a UE is 2. For example, if a PUSCH of UE #0 istransmitted using 2 TBs, sequence index #0 may be allocated to PUSCH TB#0 of UE #0 and sequence index #1 may be allocated to PUSCH TB #1 of UE#0.

Furthermore, it is possible to allocate different orthogonal sequencesto respective UEs and to respective TBs each transmitting a PUSCH ofeach UE. For example, when each of PUSCHs of UE #0 and UE #1 istransmitted using 2 TBs, sequence index #0 may be allocated to PUSCH TB#0 of UE #0, sequence index #1 may be allocated to PUSCH TB #1 of UE #0,sequence index #2 may be allocated to PUSCH TB #0 of UE #1, and sequenceindex #3 may be allocated to PUSCH TB #1 of UE #1.

The aforementioned method of generating a modulation symbol sequence isbased on the assumption of coherent detection at a UE. That is, todemodulate a modulation symbol sequence generated using theabove-described method, a UE can demodulate the modulation sequenceafter acquiring channel information using a CRS, DMRS, etc. Adescription will be given of a method of generating a modulation symbolsequence for non-coherent detection, which can be used when channelinformation is unknown (although a modulation scheme such as BPSK is notused for a sequence for non-coherent detection, the term ‘modulationsymbol sequence’ is used in the following description in order to stresscorrespondence between the modulation symbol sequence for non-coherentdetection and the aforementioned modulation symbol sequence for coherentdetection).

Methods of Generating a Sequence of ePHICH Modulation Symbols forNon-Coherent Detection

Methods of generating a modulation symbol sequence from 1-bit ACK/NACKinformation corresponding to a TB will now be described. ACK/NACKinformation for a PUSCH received from a UE can be mapped to anorthogonal sequence and then configured as a modulation symbol sequence.If an ePHICH is configured of 12 REs, the length N^(PHICH) of orthogonalsequence W can have various values such as 2, 4, 6, 12, etc. If thelength of the orthogonal sequence is 12, a modulation symbol sequencecan be determined without performing repetition. When the length of theorthogonal sequence is less than 12, repetition can be performed tocorrespond to the length of 12. A modulation symbol sequence d(i)generated in this manner can be represented by the following equation18.d(i)=w(i mod N ^(PHICH)), i=0, . . . , M _(sym)−1  [Equation 18]

FIG. 16 illustrates generation of a modulation symbol sequence using theorthogonal sequence having the normal cyclic prefix and a length of 4(N^(PHICH)) shown in Table 12. Here, sequence indexes may be previouslyset such that sequence index #0 corresponds to NACK and sequence index#1 corresponds to ACK. Orthogonal sequences corresponding to sequenceindexes #4 to #7 including imaginary components are not used because themodulation symbol sequence is for non-coherent detection. When the TBtransmitted on the PUSCH from the UE corresponds to ACK, orthogonalsequence [1 −1 1 −1] corresponding to sequence index #1 is selected.Since the length of this orthogonal sequence is 4, a length-12modulation symbol sequence can be generated through three repetitions,as shown in FIG. 16.

Alternatively, an orthogonal sequence with N^(PHICH)=12 as shown inTable 14 may be used. That is, sequence index #0 and sequence index #1that do not include imaginary elements are preset such that sequenceindex #0 corresponds to NACK and sequence index #1 corresponds to ACK inTable 14, and a modulation symbol sequence can be determined using asequence selected according to whether a reception acknowledgementresponse to the TB is ACK or NACK. Here, repetition is not performedbecause the length of the orthogonal sequence is 12.

A method of generating a modulation symbol sequence for 2 TBs will nowbe described. The 2 TBs may be transmitted on a PUSCH from a UE.Specifically, the UE may map the 2 TBs to 2 to 4 layers, precode themapped TBs and then transmit the precoded TBs through a plurality ofantennas. Otherwise, the 2 TBs may be respectively transmitted on PUSCHsof 2 UEs each using one TB.

An orthogonal sequence corresponding to a combination of ACK/NACKinformation for the 2 TBs can be selected using a mapping table such asTable 16 and Table 12.

TABLE 16 ACK/NACK bits Sequence index (TB#0, TB#1) 0 (NACK, NACK) 1(NACK, ACK) 2 (ACK, NACK) 3 (ACK, ACK)

Specifically, when a combination of ACK/NACK for 2 TBs, TB#0 and TB#1 is(ACK, NACK), sequence index #2 is set and orthogonal sequence [1 1 −1−1] corresponding to sequence index #2 may be selected from Table 12.Since the length of the selected orthogonal sequence is 4, a modulationsymbol sequence, as shown in FIG. 17, can be generated through threerepetitions corresponding to the number of REs for the ePHICH, 12.

The aforementioned modulation symbol sequence generation method may usea randomly generated scrambling sequence.

Specifically, a length-12 modulation symbol sequence d(i), i=0, . . . ,M_(sym)−1, can be generated by applying a randomly generated scramblingsequence c(i), i=0, . . . , M_(syn)−1 to a block of complex-valuedmodulation symbols z(i), i=0, . . . , M_(s)−1. This can be representedby the following equation 19.d(i)=f(c(i))·z(i),i=0, . . . , M _(sym)−1, M _(s) =M _(sym)  [Equation 19]

Otherwise, scrambling may be performed using the randomly generatedscrambling sequence when an orthogonal sequence is applied to a block ofcomplex-valued modulation symbols without spreading. This can berepresented by the following equation 20.d(i)=w(i mod N ^(PHICH))·f(c(i)·z(i), i=0, . . . , M _(sym)−1  [Equation20]

Alternatively, it is possible to spread a block of complex-valuedmodulation symbols using an orthogonal sequence and apply the randomlygenerated scrambling sequence thereto. This can be represented by thefollowing equation 21.d(i)=w(i mod N ^(PHICH))·f(c(i))·z(└i/N ^(PHICH)┘), i=0, . . . , M_(sym)−1  [Equation 21]

In equations 19 to 21, a length-31 gold sequence may be used as therandomly generated scrambling sequence c(i), i=0, . . . , M_(sym)−1 andf(·) may be an arbitrary function. Furthermore, the randomly generatedscrambling sequence may be a cell-specific or UE-specific sequence. Thatis, a cell-specific randomly generated scrambling sequence initializedusing slot number n_(s) and cell identifier N_(ID) ^(cell). In thiscase, an initial value is represented by Equation 22.c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2⁹ +N _(ID) ^(cell)

For example, in case of N_(ID) ^(cell)=4 and slot 0, the cell-specificrandomly generated scrambling sequence can be initialized withc_(init)=(2·4+1)·2⁹+4=4612 using Equation 22.

Otherwise, a UE-specific randomly generated scrambling sequenceinitialized using Equation 23 may be used.c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +n _(RNTI)  [Equation23]

Here, n_(s) denotes slot number, N_(ID) ^(cell) represents a cellidentifier, and n_(RNTI) represents C-RNTI (radio network temporaryidentifier).

For example, when N_(ID) ^(cell)=4 and the slot number is 0, a UE havinga C-RNTI of 0 can use a randomly generated scrambling sequenceinitialized with c_(init)=(2·4+1)·2¹⁶=589824 and a UE having a C-RNTI of1 can use a randomly generated scrambling sequence initialized withc_(init)=(2·4+1)·2¹⁶30 1=589825 using Equation 23.

When an orthogonal sequence is used to generate a modulation symbolsequence, different orthogonal sequences may be allocated to respectiveUEs, respective TBs or respective UEs and TBs, as described above.

Different orthogonal sequence indexes may be respectively allocated toACK/NACK information for PUSCHs and UEs such that a plurality of UEs cansimultaneously use the same resource. That is, UE multiplexing can beemployed.

For example, when UE #0 uses one TB for PUSCH transmission, sequenceindex #0 and sequence index #1 may be assigned to UE #0. When UE #1 alsouses one TB for PUSCH transmission, sequence index #2 and sequence index#3 may be assigned to UE #1. Each of UE #0 and UE #1 can use 2 sequencesallocated thereto to indicate ACK/NACK information for a PUSCH. Forexample, when PUSCH ACK/NACK information of UE #0 corresponds to NACK, asequence can be configured using sequence index #0. If the PUSCHACK/NACK information of UE #0 corresponds to ACK, a sequence can beconfigured using sequence index #1. When PUSCH ACK/NACK information ofUE #1 corresponds to NACK, a sequence can be configured using sequenceindex #2. If the PUSCH ACK/NACK information of UE #1 corresponds to ACK,a sequence can be configured using sequence index #3.

It is possible to simultaneously transmit ACK/NACK information for amaximum of 2 TBs that can be transmitted by a UE using the same resourceby respectively allocating different orthogonal sequence indexes toPUSCH TBs of the UE and PUSCH ACK/NACK information of each TB.

For example, when a PUSCH of UE #0 is transmitted through 2 TBs, ifsequence index #0 (in case of NACK) and sequence index #1 (in case ofACK) are allocated to PUSCH TB #0 of UE #0 and sequence index #2 (incase of NACK) and sequence index #3 (in case of ACK) are allocated toPUSCH TB #1 of UE #0, ACK/NACK for PUSCH TB #0 and ACK/NACK for PUSCH TB#1 can be simultaneously transmitted using the same resource.

It is possible to simultaneously transmit ACK/NACK information for TBstransmitting PUSCHs from a plurality of UEs using the same resource byallocating orthogonal sequence indexes depending on the TBs transmittingthe PUSCHs of the UEs and ACK/NACK bits of the TBs.

For example, when PUSCHs of UE #0 and UE #1 are transmitted using 2 TBs,sequence index #0 (in case of NACK) and sequence index #1 (in case ofACK) can be allocated to PUSCH TB #0 of UE #0 and sequence index #2 (incase of NACK) and sequence index #3 (in case of ACK) can be allocated toPUSCH TB #1 of UE #0. Similarly, sequence index #4 (in case of NACK) andsequence index #5 (in case of ACK) can be allocated to PUSCH TB #0 of UE#1 and sequence index #6 (in case of NACK) and sequence index #7 (incase of ACK) can be allocated to PUSCH TB #1 of UE #1. Otherwise,sequence indexes #0 to #3 can be allocated to 2 TBs of UE #0 accordingto ACK/NACK combinations of PUSCH TB #0 and PUSCH TB #1 of UE #0, asshown in Table 16, whereas sequence indexes #4 to #7 can be allocated to2 TBs of UE #1 according to ACK/NACK combinations of PUSCH TB #0 andPUSCH TB #1 of UE #1.

A sequence generated using the aforementioned method may be multiplexedfor UEs.

ACK/NACK for PUSCH TBs of a plurality of UEs can be simultaneouslytransmitted. For example, a sequence generated from ACK/NACK for thefirst TB of UE #0 according to the aforementioned method and a sequencegenerated from ACK/NACK for the first TB of UE #1 according to theaforementioned method can be summed and transmitted.

ACK/NACK for 2 PUSCH TBs of a UE can be simultaneously transmitted. Forexample, a sequence generated from ACK/NACK for the first TB of UE #0according to the aforementioned method and a sequence generated fromACK/NACK for the second TB of UE #0 according to the aforementionedmethod can be summed and transmitted.

ACK/NACK for 2 PUSCH TBs of a plurality of UEs can be simultaneouslytransmitted. For example, a sequence generated from ACK/NACK for thefirst TB of UE #0, a sequence generated from ACK/NACK for the second TBof UE #0, a sequence generated from ACK/NACK for the first TB of UE #1,a sequence generated from ACK/NACK for the second TB of UE #1 can besummed and transmitted.

Methods of Mapping a Sequence of ePHICH Modulation Symbols

A description will be given of methods of mapping modulation symbolsequences generated through the aforementioned methods to RBs and/orREs. A modulation symbol sequence mapped to REs may be obtained throughmapping to one or more layers and precoding. While the REs to which themodulation symbol sequence is mapped may be located in a control regionof a subframe, like a conventional PHICH resource region, the REs arepositioned in a PDSCH region, that is, a resource region other than anOFDM symbol region indicated by a PCFICH in the following description.Furthermore, a PHICH group used in LTE/LTE-A systems may be applied.

According to a first embodiment of mapping a modulation symbol sequenceto REs, the modulation symbol sequence can be mapped to REs of a PDSCHregion other than a PDCCH region in an RB allocated to a UE that willreceive an ePHICH. Here, the UE can detect a PHICH corresponding to theentire frequency region of the RB allocated thereto or to part of thefrequency region because the UE is aware of the position of the RBallocated thereto. Accordingly, it is not necessary to additionallysignal a resource region to the UE.

FIG. 18 illustrates a scheme of mapping a modulation symbol sequence toan RB allocated to a specific UE. Referring to FIG. 18, a modulationsymbol sequence generated from ACK/NACK information for one or more TBstransmitted from the specific UE can be mapped to the RB allocated tothe specific UE in the direction of frequency axis, as shown in FIG. 18.

According to a second embodiment of mapping a modulation symbol sequenceto REs, the modulation symbol sequence can be mapped to a resourceregion of an RB allocated to a UE other than the UE that will receivethe ePHICH or to an RB allocated to a specific UE and an RB allocated toa UE other than the specific UE. This may be performed when multiplexedUEs use the same resource. In this case, the corresponding UE needs toknow the positions of REs mapped to the ePHICH in order to detect theePHICH from an RB other than the RB allocated to the UE. To achievethis, the RE position may be signaled to the UE through higher layersignaling, or a predefined region may be used. If the positions of REsmapped to a modulation symbol sequence are signaled through higher layersignaling, a PDCCH, etc., an OFDM symbol index at which mapping isstarted can be signaled or the OFDM symbol index and a subcarrier indexcan be signaled together. Methods of mapping a modulation symbolsequence to an RB according to the second embodiment will now bedescribed with reference to FIGS. 19 to 22.

FIG. 19 is a diagram illustrating a scheme for sequentially mappingsymbols of a modulation symbol sequence in the frequency domain. Here,the RB may be an RB allocated to a UE other than the specific UE, asdescribed above.

Referring to FIG. 19(a), it can be seen that the start OFDM symbol index(here, the start OFDM symbol index may be explicitly signaled to the UEor may be blind-detected by the UE using a cell identifier, etc.) is 3and mapping is performed with a subcarrier index sequentially increasingfrom 0 when the ePHICH is frequency-preferentially mapped. In this case,it is assumed that a PDCCH uses 3 OFDM symbols.

FIG. 19(b) shows that the start OFDM symbol index is 4 and mapping isperformed using the entire band of the RB. Referring to FIG. 19(b),sequential mapping is performed in the frequency domain, starting fromOFDM symbol index #4 and subcarrier index #0 and REs to which RSs aremapped are excluded. While 12 symbols of the modulation symbol sequenceneed to be mapped, symbols of the modulation symbol sequence, which areleft without being mapped to the fourth OFDM symbol, may be mapped tothe next OFDM symbol, that is, the fifth OFDM symbol since the REsmapped to the RSs are excluded. Here, mapping to the fifth OFDM symbolmay be performed starting from subcarrier index #0 as shown in the leftpart of FIG. 19(b), or performed starting from subframe index #11 asshown in the right part of FIG. 19(b).

FIG. 19(c) illustrates a case in which the start OFDM symbol index is 4and mapping is performed using the entire bands of 2 RBs in case offrequency-preferential mapping (while 2 RBs are used in this embodiment,two or more RBs can be used and one or more RBs may be located betweenRBs). In this case, the start OFDM symbol index may be set depending onthe cell identifier of the corresponding cell such that the mappedresource region does not considerably interfere with a resource regionused for ePHICH transmission in a neighboring cell. For example, an REregion used for mapping, shown in FIG. 19(c), is prevented from beingused for mapping in a cell other than the corresponding cell (throughnulling, for example) to reduce the influence of interference. The startsymbol index can be determined according to cell ID mod 6, for example.

FIG. 20 illustrates schemes of mapping symbols of a modulation symbolsequence to contiguous REs in the time domain.

Referring to FIG. 20(a), when a modulation symbol sequence includes 12symbols, the symbols are sequentially mapped in the first slot of asubframe in the time domain. Specifically, referring to the left part ofFIG. 20(a), the start OFDM symbol index is 3, the start subcarrier indexis 0, and mapping is performed for the first slot with the OFDM indexincreasing in the time domain. Here, if mapping is not completed, thesubcarrier index is increased and mapping is carried out.

The right part of FIG. 20(a) shows that the start OFDM symbol index is 4and the start subcarrier index is 0, similarly to the left part of FIG.20(a). However, when the subcarrier index is increased, the OFDM symbolindex mapped before the subcarrier index is increased is maintained,distinguished from the case shown in the left part of FIG. 20(a).

A mapping method shown in the left and right parts of FIG. 20(b)corresponds to the mapping method shown in FIG. 20(a), except that thestart subcarrier index is 3. In this case, REs to which RSs are mappedare excluded from mapping.

FIG. 20(c) shows a scheme for mapping symbols of a modulation symbolsequence with the OFDM symbol index increasing in the time domain for asubframe. In this case, the start OFDM symbol index is 3 and the startsubcarrier index is 0. Referring to the left part of FIG. 20(c), thesymbols of the modulation symbol sequence are sequentially mapped to onesubframe, with the OFDM symbol index sequentially increasing from theOFDM symbol following an OFDM symbol index at which the PDCCH is ended,when the start subcarrier index is 0. Here, when the start subcarrierindex is 0, the symbols of the modulation symbol sequence are notcompletely mapped to 12 REs. Thus, the subcarrier index is increased,and then mapping is performed on OFDM symbols other than OFDM symbolsused as a control region, with the OFDM symbol index sequentiallyincreasing. This operation is repeated until all the 12 REs are mapped.Referring to the right part of FIG. 20(c), the ePHICH is mapped to OFDMsymbols to occupy one subframe, with the OFDM symbol index sequentiallyincreasing from the OFDM symbol following an OFDM symbol index at whichthe PDCCH is ended, when the start subcarrier index is 0. Here, when thestart subcarrier index is 0, all 12 REs are not mapped. Thus, thesubcarrier index is increased, and then mapping is performed with theOFDM symbol index sequentially increasing from OFDM symbol index #6 ofthe second slot. This operation is repeated until all symbols aremapped.

FIG. 20(d) illustrates a mapping scheme similar to the mapping schemeshown in FIG. 20(c) except that the start subcarrier index is 3. In thiscase, the start subcarrier index may be set depending on the cellidentifier of the corresponding cell such that a resource for mappingdoes not considerably interferes with a resource used for ePHICHtransmission in a neighboring cell. Here, it is possible to alleviateinterference with the neighboring cell by transmitting no signal usingREs corresponding to the resource for ePHICH transmission in theneighboring cell. Furthermore, a selected RB may be allocated dependingon the cell identifier. If the position of the RB is set depending onthe cell identifier even when an ePHICH is transmitted in the sameregion as that used for mapping in the RB, the influence of interferencefrom the ePHICH of the neighboring cell can be reduced. In this case,the RB may be determined according to cell ID mod 6, for example, orhigher layer signaling (RRC signaling). At this time, the ePHICHresource region used in the neighboring cell may be nulled. The positionof the resource region may be determined according to cell ID mod 6, forexample, or higher layer signaling (RRC signalling). In this case, ratematching of a PDSCH or a PDCCH may be needed.

FIG. 21 illustrates methods of frequency-first mapping symbols of amodulation symbol sequence to REs which are discretely contiguous in thefrequency domain.

FIG. 21(a) shows a mapping scheme on the basis of a group of 4contiguous REs when the start OFDM symbol index is 4 and startsubcarrier index is 0. Specifically, the left of FIG. 21(a) shows ascheme for mapping modulation symbols with the subcarrier indexsequentially increasing when the start OFDM symbol index is 4. When all12 symbols are not mapped at the OFDM symbol sequence #4, the OFDMsymbol index is increased, and then mapping is performed with thesubcarrier index increasing from 0 until mapping is completed. The rightpart of FIG. 21(a) is distinguished from the left part of FIG. 21(a) inthat mapping is performed with the subcarrier index decreasing when theOFDM symbol index is increased.

FIG. 21(b) shows a mapping scheme depending on a cell identifier toreduce interference with an ePHICH transmitted in a neighboring cell. Inthis case, the start subcarrier index may be determined using cell IDmod 6, for example, or higher layer signaling (RRC signaling). WhileFIG. 21(b) illustrates that symbols are mapped to 3 RBs, one or more RBsmay be positioned between neighboring RBs of the 3 RBs because the RBsare allocated to the UE according to distributed resource allocation.Here, the 3 RBs may be assigned depending on the cell identifier of thecorresponding cell to reduce interference with the ePHICH from theneighboring cell. In this case, the position of the resource region maybe determined by cell ID mod 6, for example, or higher layer signaling(RRC signaling).

Specifically, FIG. 21(b) shows a mapping method for alleviatinginterference between two cells (cell 0 and cell 1). That is, mapping isperformed on a group of 4 contiguous REs in the frequency domain foreach RB at start OFDM symbol index #3 and start subcarrier index #0 incell 0, and mapping is performed on a group of 4 contiguous REs in thefrequency domain for each RB at start subcarrier index #4 in cell 1. Inthis case, interference between cell 0 and cell 1 can be reduced. Thestart subcarrier index of each cell may be determined using cell ID mod6, for example, or higher layer signaling (RRC signaling).

FIG. 21(c) illustrates a mapping scheme for reducing inter-cellinterference like the mapping scheme shown in FIG. 21(b). Referring toFIG. 21(c), mapping is performed frequency-preferentially for subcarrierindexes #0 to #3 in cell 0, and mapping is carried outfrequency-preferentially for subcarrier indexes #4 to #7 in cell 1.

FIG. 22 illustrates methods of mapping symbols of a modulation symbolsequence to discretely contiguous REs time-domain-preferentially.

Referring to FIG. 22(a), mapping is started at OFDM symbol #4 andsubcarrier symbol #3 and performed in such a manner that symbols aremapped to 4 contiguous REs in an RE group, the following 4 REs areskipped, and then symbols are mapped to the following 4 contiguous REsin a group. More specifically, the left part of FIG. 22(a) shows thatmapping is performed with the OFDM symbol index increasing in thedirection of the time domain when the subcarrier index increases whereasthe right part of FIG. 22(a) shows that, when the subcarrier indexincreases, mapping is performed in a direction opposite to the mappingdirection corresponding to the previous subcarrier index.

Referring to FIG. 22(b), mapping is performed on the resource region ofthe second slot in addition to the resource region of the first slot,distinguished from the mapping method shown in FIG. 22(a), whichperforms mapping on only the resource region of the first slot.

FIG. 22(c) illustrates a mapping scheme depending on a cell identifierto reduce interference with an ePHICH transmitted in a neighboring cell.In this case, the start subcarrier index may be determined according tocell ID mod 6, for example, or higher layer signaling (RRC signaling).While FIG. 22(c) shows that symbols are mapped to 3 RBs, one or more RBsmay be positioned between neighboring RBs of the 3 RBs because the RBsare allocated to the UE according to distributed resource allocation.Here, the 3 RBs may be assigned depending on the cell identifier of thecorresponding cell to reduce interference with the ePHICH from theneighboring cell. In this case, the position of the resource region maybe determined by cell ID mod 6, for example, or higher layer signaling(RRC signaling).

Specifically, FIG. 22(c) shows a mapping method for alleviatinginterference between two cells (cell 0 and cell 1). That is, mapping isperformed on a group of 4 contiguous REs in the time domain for each RBat start OFDM symbol index #3 and start subcarrier index #0 in cell 0,and mapping is performed on a group of 4 contiguous REs in the timedomain for each RB at start subcarrier index #4 in cell 1. In this case,interference between cell 0 and cell 1 can be reduced. The startsubcarrier index of each cell may be determined using cell ID mod 6, forexample, or higher layer signaling (RRC signaling).

According to a third embodiment, a modulation symbol sequence can bemapped to a resource region other than the control region in the systembandwidth. That is, the first and second embodiments perform mapping onsome of RBs corresponding to the entire system bandwidth, whereas thethird embodiment performs mapping on all RBS included in the entiresystem bandwidth.

FIG. 23(a) illustrates a scheme for mapping a modulation symbol sequenceto specific OFDM symbols in the system bandwidth. In FIG. 23(c), thesystem bandwidth corresponds to 4 RBs. Specifically, mapping isperformed at start OFDM symbol index #3 and start subcarrier index #0 inthe system bandwidth. In this case, mapping may be performed on aresource region based on the cell identifier in order to reduceinterference with a neighboring cell. To prevent mapping frominterfering with an ePHICH resource used in the neighboring cell, REs atthe same positions as that of the ePHICH region allocated to theneighboring cell may be nulled. Here, rate matching of a PDSCH or aPDCCH may be needed.

Referring to FIG. 23(b), when the start OFDM symbol index is 3 in thesystem bandwidth, 12 REs for ePHICH transmission are divided into groupseach including 4 REs and mapping is performed on each RE group with thesubcarrier index increasing from 0. Here, the position of a resource forePHICH transmission may be determined by the cell identifier or thesystem bandwidth. In this case, in order to reduce interference from theePHICH resource allocated in the neighboring cell, a different resourcemay be assigned on the basis of the cell identifier. To prevent mappingfrom interfering with the ePHICH resource used in the neighboring cell,REs at the same positions as that of the ePHICH region allocated to theneighboring cell may be nulled. Here, rate matching of a PDSCH or aPDCCH may be needed.

In the mapping methods shown in FIGS. 23(a) and 23(b), the positions ofREs may be signaled to the UE through higher layer signaling, or apredefined region may be used. If the positions of REs mapped to themodulation symbol sequence are signaled through higher layer signaling,a PDCCH, etc., an OFDM symbol index at which mapping is started may besignaled, or the OFDM symbol index and a subcarrier index may besignaled together.

In the above-described embodiments, the start OFDM symbol index and/orthe start subcarrier index may be determined such that they are closestto an RE carrying a RS. For example, the start OFDM symbol index can be0 and the start subcarrier index can be 2 in FIG. 21(c). In this case,accuracy of demodulation of an ePHICH can be, improved through moreaccurate channel estimation.

A modulation symbol sequence mapped to REs according to theabove-described methods may be demodulated through coherent detection ornon-coherent detection. When a UE uses coherent detection, the UE mayperform channel estimation using a CRS, DMRS or the like and demodulatean ePHICH based on the channel estimation result when attempting todetect the ePHICH. This case can correspond to the method for mapping anePHICH of a specific UE to an RB allocated to the specific UE, fromamong the aforementioned methods. Accordingly, when the ePHICH is mappedto a region on an RB allocated to a UE other than the specific UE ormapped to the entire system bandwidth, non-coherent detection can beused. Even when the ePHICH is configured by multiplexing ACK/NACK forPUSCHs of a plurality of UEs, a UE can detect the ePHICH from an RB thatis not allocated to the UE using non-coherent detection since channelestimation is not needed.

FIG. 24 illustrates configurations of an eNB and a UE according to anembodiment of the present invention.

Referring to FIG. 24, the eNB 2410 may include a reception module 2411,a transmission module 2412, a processor 2413, a memory 2414, and aplurality of antennas 2415. The plurality of antennas 1815 representsthat the eNB 2410 supports MIMO transmission/reception. The receptionmodule 2411 may receive signals, data and information on uplink from theUE. The transmission module 2412 may transmit signals, data andinformation to the UE on downlink. The processor 2413 may control theoverall operation of the eNB 2410.

The processor 2413 of the eNB 2410 precodes a codeword including DCIusing one of precoding matrices included in a candidate precoding matrixset of the codebook. The UE may need to attempt to de-precode theprecoding matrices included in the candidate precoding matrix set forthe DCI.

In addition, the processor 2413 of the eNB 2410 may process informationreceived by the eNB 2410, information to be transmitted to the outside,etc. The memory 2414 may store the processed information for apredetermined time and may be replaced by a component such as a buffer(not shown).

The UE 2420 may include a reception module 2421, a transmission module2422, a processor 2423, a memory 2424, and a plurality of antennas 2425.The plurality of antennas 2425 represents that the UE 2420 supports MIMOtransmission/reception. The reception module 2421 may receive signals,data and information on downlink from the eNB. The transmission module2422 may transmit signals, data and information on uplink to the eNB.The processor 2423 may control the overall operation of the UE 2420.

The processor 2423 of the UE 2420 may attempt to perform de-precodingusing precoding matrices included in the candidate precoding matrix setof the codebook for DCI in a predetermined resource region of asubframe.

The processor 2423 of the UE 2420 may process information received bythe UE 2420, information to be transmitted to the outside, etc. Thememory 2424 may store the processed information for a predetermined timeand may be replaced by a component such as a buffer (not shown).

The detailed configurations of the eNB and the UE may be implementedsuch that the aforementioned embodiments of the present invention can beindependently applied thereto or two or more embodiments can besimultaneously applied thereto, description of redundant parts isomitted for clarity.

Description of the eNB 2410 in FIG. 24 may be equally applied to anapparatus as a downlink transmitter or an uplink receiver anddescription of the UE 2420 may be equally applied to a relay as adownlink receiver or an uplink transmitter.

The detailed configurations of the eNB and the UE may be implementedsuch that the aforementioned embodiments of the present invention can beindependently applied thereto or two or more embodiments can besimultaneously applied thereto, description of redundant parts isomitted for clarity.

Description of the eNB 1810 in FIG. 24 may be equally applied to anapparatus as a downlink transmitter or an uplink receiver anddescription of the UE 1820 may be equally applied to a relay as adownlink receiver or an uplink transmitter.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof.

In a hardware configuration, the methods according to the embodiments ofthe present invention may be achieved by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, the embodiments of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. For example, software code may be stored in a memory unitand executed by a processor. The memory unit is located at the interioror exterior of the processor and may transmit and receive data to andfrom the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an exemplary embodiment of thepresent invention or included as a new claim by a subsequent amendmentafter the application is filed.

INDUSTRIAL APPLICABILITY

While the present invention is applied to 3GPP LTE mobile communicationsystem in the above description, the present invention can be used invarious mobile communication systems based on the same or equivalentprinciple.

The invention claimed is:
 1. A method for mapping an extended physicalhybrid automatic repeat request (ARQ) indicator channel (ePHICH) in awireless communication system, the method comprising: determining one ormore resource blocks to which the ePHICH for a user equipment (UE) willbe mapped; and mapping a plurality of modulation symbols for the ePHICHto a plurality of resource elements included in the resource blocks,wherein the resource elements are positioned in regions other thanorthogonal frequency division multiplexing (OFDM) symbol regionsindicated by a physical control format indicator channel (PCFICH),wherein a modulation scheme for the modulation symbols is determinedbased on whether the resource blocks for the ePHICH include a resourceblock for another UE other than the UE receiving the ePHICH.
 2. Themethod according to claim 1, wherein the resource blocks are allocatedto the UE that receives the ePHICH.
 3. The method according to claim 1,wherein the resource blocks include a resource block that is notallocated to the UE receiving the ePHICH.
 4. The method according toclaim 1, wherein the resource blocks correspond to all resource blocksincluded in a corresponding frequency band.
 5. The method according toclaim 1, wherein a start index of the resource elements to which theplurality of modulation symbols are mapped is determined depending on acell identifier.
 6. The method according to claim 1, wherein the mappingof the plurality of modulation symbols comprises sequentially mappingthe plurality of modulation symbols to the plurality of resourceelements in the frequency domain or in the time domain.
 7. The methodaccording to claim 1, wherein the mapping of the plurality of modulationsymbols comprises grouping the plurality of modulation symbols into aplurality of groups each including n modulation symbols, and mapping theplurality of groups to the plurality of resource elements in thefrequency domain or in the time domain.
 8. The method according to claim7, wherein each of the plurality of groups is mapped with n resourceelements intervals in the plurality of resource elements.
 9. The methodaccording to claim 1, wherein the mapping of the plurality of modulationsymbols comprises mapping the modulation symbols to resource elementsadjacent to resource elements mapped to reference signals in theresource blocks.
 10. The method according to claim 1, wherein, when theresource blocks are not allocated to the UE receiving the ePHICH,information about at least one of an OFDM symbol or a subcarrier inwhich mapping of the resource elements is started is transmitted to theUE.
 11. The method according to claim 1, wherein the plurality ofmodulation symbols are generated from reception acknowledgement for oneor more transport blocks.
 12. The method according to claim 1, whereinthe one or more transport blocks are mapped to two or more layers andtransmitted on a physical uplink shared channel.
 13. The methodaccording to claim 1, wherein the modulation scheme for the modulationsymbols is determined based on a type of a reference signal applied tothe resource blocks.
 14. The method according to claim 13, themodulation scheme comprises a coherent modulation and a non-coherentmodulation.
 15. An eNB in a wireless communication system, comprising: atransmission module; and a processor, wherein the processor isconfigured to determine one or more resource blocks to which an extendedphysical hybrid automatic repeat request (ARQ) indicator channel(ePHICH) for a user equipment (UE) will be mapped and to map a pluralityof modulation symbols to a plurality of resource elements included inthe resource blocks, wherein the resource elements are positioned inregions other than orthogonal frequency division multiplexing (OFDM)symbol regions indicated by a physical control format indicator channel(PCFICH), wherein a modulation scheme for the modulation symbols isdetermined based on whether the resource blocks for the ePHICH include aresource block for another UE other than the UE receiving the ePHICH.16. The method according to claim 14, wherein the coherent modulation isused for the modulation symbols when the resource blocks for the ePHICHinclude the resource block for the another UE other than the UEreceiving the ePHICH or the reference signal is a cell-specificreference signal.
 17. The method according to claim 14, wherein thenon-coherent modulation is used for the modulation symbols when theresource blocks for the ePHICH do not include the resource block for theanother UE other than the UE receiving the ePHICH and the referencesignal is a UE-specific reference signal.